Can excessive neck clearance cause over pressure??

[AKShooter]

Well, I could not really get any light shedded on problem from my smith. He did tell me the neck length is a spec 7saum. It is a match chamber so he told me it is tight. They fired the rifle without incident. Had no insight regarding why mouth of case would be smaller. They also do not have a print on the reamer.

Anyway, here is how I'll proceed. Basically back to scratch. Headed after work to see if I can get some of the hordany headspace gauges. From there I can at least determine how forward the shoulder moved on the case I have.

(worth noting what I saw as pressure signs, primer was fine, not flattened, but basically after the shot had a hard bolt lift, bits of brass actually welded the ejector down, didn't take much to free it, then a smudge of brass coming off ejector. Case has a ejector mark on back of case)

Then look back at loads. Make sure of my to land measurement, pretty sure thats good to go though, I can cycle loaded ammo and OAL remains the same, certainly not pulling bullets.

On the 300saum brass, make sure I'm using correct case holder, look at die,

Unload the powder in the other rounds I have, do a visual inspection to H4831SC on hand, its certainly worth a check. Same on primers, just going to de-cap the 50, now 49 I've done. Just to make sure its not a mag primer, I load those too.

Maybe look at slower reccomended powders, also have a different jug of 4831 I can try.

Just has me baffled, custom gun, can't imagine having pressure signs with middle road loads.

Some of you guys mentioned that custom guns need loads worked up, I agree. But I currently own 6 centerfires, 3 remington 700's and 2 savages. Everyone of them ran to max without pressure signs, now some didn't shoot the best at max, so accuracy load is lower for the 2 or 3.

Any insight on why a rifle would see excessive pressure and low to starting powder charges??

 

[ar10ar15man]

the 2.0 length you list aint quite right......
2.0 means anything from 2.0049 and down using std rounding....
the case needs to be 2.001 for ideal, technically out to 2.035.....
but with your issues i would try a case just short of design...say 1.990,,and see what happens.
buy the 7mm neck slug from sinclair and find out how long the neck actually is

not likely a primer issue.....

like i said before..its not a FACTORY RIFLE...quit acting like it is...start LOW and work up

 

[AKShooter]

ar15ar10man

No, I get the point, just crying in my beer.

Aand you are correct, case dimension on the factory brass is 2.025. The sized 300 brass is more like 2 even, I'll remeasure tonight.

 

[Toby Bradshaw]

Don't fool with the primers -- they're fine. If you are getting enough pressure to flow brass into the ejector hole, changing the primer isn't going to help anyway. Just drop the charge weight and be sure that all loaded rounds are at least 0.002 smaller than the 0.320 chamber neck dimension. If you want to be extra careful, cycle the loaded rounds through your action (with the firing mechanism removed from the bolt) to be sure that they chamber easily.

If you chronograph your loads you'll probably find that a reduced load still gives the same (or better) velocity as factory ammo.

 

[AKShooter]

Well, I was able to figure out why my 300saum brass was not chambering, just don't know the fix.

I removed the ejector, button, saw some brass around edge. Wanted to hit it wit some copper cleaner too.

Anyway, its off, went and inserted a piece of necked 300saum brass, fed it up through the action, with case head square to bolt, snapped into extractor.

Chambers fine, I figured something else was the issue since the neck junction is less on the 300, you are basically fire forming 300 to 7.

Anyway, the ones I somewhat forced to chamber (prior to ejector removal) left a pretty decent extractor mark, width of extractor on rim.

While maybe not related to my other problem in this thread, but again, another issue. Well just another symptom,,, Its a sako style extractor, I have a local smith, maybe I'll see what his thoughts are.

but other thoughts are welcome

 

[pcrowe]

I had a problem similar to this once on a new 6.5x284 barrel. Don't know what reamer was used, but I was sizing brass with my Redding bushing die (wanted to be able to control neck tension) and was seeing pressure signs too early. Finally determined that I have to size the brass with a full length Hornady sizer. Brass sized with the Hornady die was about half a thou smaller just above the web and the pressure signs went away. Brass sized with either die would chamber fine. No sweat on using the Hornady full length sizer as my ammo loaded this way shoots very well.

Good luck, let us know if you find your solution.

 

[AKShooter]

Well, went to discuss with a professional.

Here is what I know. The reason the 300saum is getting hung up and not chambering is the case head is about 4 thousand larger than the remington 7 saum. With some wet dry and a polish with steel wool, cleared that all up.

As the the over pressure, this gunsmith said he sees the overpressure pretty commonly with the short mags, he said they take some time to shoot in.

His reccomendation would be to go back to min, or a little less, and make sure I'm shooting over a chrono and document it.

So thats what I'm doing, sinclair was out of th 7mm plug for neck thickness, but thats something I'll follow-up too.

I'll be sure to post back with results, you guys have been great, don't want to leave you hanging, it will take a bit of time though, need to now get back to the range, and I can't really make that happen during the week,,,,desk jockey!!

 

[Three44s]

...............................................................

On the turning, from pics feel I cut well down into shoulder

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Thanks

To me it sounds like a short distance from the bolt face to the case mouth with in your chamber. I have seen a couple of factory rifles of the same brand have this problem in .22-250. I just shortened the brass a little more.

The way I diagnosed it was looking at the mouth of a freshly fired case and seeing irregular bright marks on the leading edge of the case mouth.

I included your comment on turning your the exterior of your case necks a little too deep. It seems to me that could cause your case length to grow .... ie. the cases stretching from the weakened shoulder/neck junction.

If that's the situation, it could be exacerbating a short chamber at the case mouth.

Best regards

Three 44s

 

[R.Morehouse]

Well, the hits keep coming

I just tried to chamber some neck turned 300 nosler brass. It will not chamber. All I did to the brass was ran it through a full size Rcbs die. Then a k&m expander Ran it back through the FL die. Still wont chamber. What now? Body die? Any thoughts.

Starting to feel like more than a novice here

On the turning, from pics feel I cut well down into shoulder

From here, going to cut down some rem 7saum brass to 300 saum oal brass and go from there.

Thanks

I just went through the same stuff with Nosler brass. My custom 300RUM with 92g Retumbo was sticking the bolt ect. and going 3050. I thought I was going with the "GOOD" brass for my 1st custom. The necks were way out and needed turned but that did nothing for me. Went and got a bag of Rem brass and loaded up 2 each 92-92.5-93.-93.5-94-94.5. All ejected perfectly with just the first sign of cratering of the primer at 94.5. Giong to be a nice weekend here in Pa. so out comes the crono. to see what I got and to start finding my load.

 

[searcher]

A few thoughts in addition to the other folks. When you chamber a round, any resistance felt over that of an unloaded chamber could be a clear indicator of excessive brass length - aside from/in addition to lack of neck clearance. If you are unsure of your measurements and do feel resistance when closing the bolt over that of an emply chamber, trim a test case .010", chamfer and retry chambering. If condition persists, redo this two more times to rule out excessive length.

You want at least .002" to .003" neck clearance between loaded round and neck area of chamber. I recommend pouring a chamber casting to see what you really have. Not rare for custom guns to be as much as a few thousandths off. Buy some Cerrosafe from Brownell's and pour into chamber as per the provided directions and be sure. If you have ruled out excessive brass length and still feel resistance when closing bolt, will be due to lack of neck clearance most likely. (Could also be lack of proper headspace but less likely in this scenario) Compare the chamber casting with your loaded ammo neck and you will know for sure.

If you have pushed your shoulder back excessively when sizing (if bumping shoulder or full-length resizing), the cartridge slamming into the face of the bolt can mimic signs of high pressure, pop and flatten primers, etc. . Make sure sizing die set up to push shoulder back only .002" or so. Can use Hornady Lock N Load headspace measuring tool for this.

If you are using a real slow burning powder and too-light loads, symptoms of excessive pressure can develop as well. Remedy would be to SLOWLY increase powder amount but only after ruling out the above items! Due to an error in a Barnes manual, I almost blew up my .375 H&H magnum due to this. (They since corrected the manual)

 

[AKShooter]

UPDATE: I do feel the neck cut is not spec deep, I ended up trimming back my modified case, it was @ 2.29. Trimmed back to 2.09, was able to get repeatable "to land" measurements, before that it was difficult to seat the case, and get repeatable measurements (sinclair has 7mm gauge backordered)

We had some bad weather move through, but did end up with a window from the weather and my life this morning, not a planned trip so didn't have my chrono.

I am still in the break in, so really just wanted to safely put some rounds through it so I can get through the barrel break in. (really wish I had the chrono)

Range for H4831SC in the Nolser manual is 55.5 - 59.0 (for the record my only other round fired was at 57.5) I loaded three powder charges, 54.5,55.0 and 55.5, Used resized 300SAUM brass since the case is shorter than factory 7. Had untrimmed NORMA and trimmed Nosler. Loaded the NORMA was .315 at neck and the .311

First round was the trimmed nosler, 54.5, first round left a sticky bolt. Extractor mark. Damn.

Figured I'd send the Norma, untrimmed NORMA faired well, no hard bolt, cases looked fine. Went ahead and did the shoot, clean, with the three I had. Went ahead and stepped up the the NORMA at 55.0, left slight extractor mark, kind of a tough bolt lift. For sure max load (and fellas, it was 27 degrees!!)

So first off, now going to step back even faurther from MIN, to the low 50's , how much down from low is safe too, Actually figured I'd go to 50 even?

So now looking at fired rounds, necks measured around 3.17, no damage or marks on front of case, think I'm in the neck area. The fired round at shoulder measures around .003 larger.

Things on my to do list, follow up with smith, he never got back to me regarding neck depth, get some cerasafe (SP) from midway for a chamber cast,,,,,,also the lock in load hordany set so I can measure loaded and fired cases.

Also, I've chambered and set barrels on quite a few savages, I've always shot for min headspace, typically I like to have the bolt close easy on a go, and basically not even start on a no-go, or just barely.

I do not have gauges for 7saum, but on a sized 7saum remington brass, I put 1 layer of painters tape, chamber fine, went to two, chambered, but tough bolt close.

I guess, going to add getting headspace checked to my list, also check same experiement on a couple other rifles.

5 rounds by me, and some by smith (unknown count) he did say there were no issues, barrel is still copper fouling heavy. but the norm for me with past rifles at this round count

Thanks

 

[Toby Bradshaw]

If the bolt closes easily on your loaded rounds you don't have a short headspace problem. But you definitely have a pressure problem if you're getting brass to flow into your ejector (not extractor), making the bolt hard to lift.

1) Remind us what bullet you're shooting.

2) Are you sure you have the right powder?

3) Check your neck length with a chamber cast if your Sinclair tool doesn't show up.

4) When describing your measurements pay attention to the decimal places. The trim length of the 7 SAUM is 2.035. When you write that your brass is 2.29 do you mean 2.029?

5) Does the Remington factory ammo still work fine? If so, that's an important clue that something is wrong with your handloads. You *could* try reloading one of the Rem cases that is working fine. However, it's a bit scary that you are getting serious pressure signs with light-ish handloads but no pressure signs (right?) with factory ammo.

 

[AKShooter]

Toby, going to start with 5)

5) I have never put a factory round down the tube, decent place to start, have not bought any pre-loaded cenerfire ammo in 5 years. But again, good idea. If this continues with factory loaded ammo, I'm inclined to have it shipped back to smith to correct, test firing was with handloads per smith

1) Shooting a nosler accubond 160, also have some 150 Nolser ballistic tips to try

2) Powder, shooting H4831SC, a recomended powder for the 7saum. I have some additonal powders on the published loads I can try

3) Chamber cast is in order, I can hopefully have something by end of week

4) point taken, and you are correct, meant to say 2.029.

Again, I'll go over everything on my end, just getting kind of bummed, need to fill in blanks like the chrono speeds, headspace , etc, just first time I've had this issue, going on around 10 rifles or so? Not many for most, but just saying I've done this sucessfully for many thousands of rounds. Something is up, just trying to get to the bottom of it.

Thanks

 

[Toby Bradshaw]

Didn't you say that you have another lot of 4831 that you could try? I'd load up one or two rounds of that. Start low.

I wouldn't be enthusiastic about buying factory ammo, either, but if that does work without pressure signs, you're well on the way to sorting this out. If factory ammo DOES show serious pressure signs, then there really is something wrong with your chamber.

Stick with it!

P.S. Check your powder scale. If you don't have a check weight, use a bullet (or, better yet, several different weight bullets). Bullets are generally very close to the weight printed on the box.

Also, measure the diameter at the mouth of a long-ish (2.030 or so) EMPTY case before and after chambering. The measurements should be the same unless the case mouth is getting pinched by a short-necked chamber. Look for rub marks on the end of the case mouth. You can put machinist's dye or Sharpie marker on the end of the case mouth. The case mouth must be deburred before taking this measurement.

 

[edlongrange]

From Lynn:

"AkShooter

Primers,neck tension,and bullet seating depth have a smaller influence on pressure than most people think and are very unlikely to be your problem. If your brass feeds into the chamber easily I would rule them out. Likewise your trim length is rarely an issue but easily confirmed. Simply cut off a large amount of the neck on one case like 0.030 and see what happens.

On a custom build the first thing that should jump right out is your chambers freebore length. If the gun was set-up for lightweight bullets with a very short freebore and your using real heavy bullets you will see pressure signs earlier. You can still shoot the same velocities but your powder charges will be different than your reloading manual lists. Most reloading manuals list the brand of brass the primer used and the loaded rounds over-all length. If you had a chronograph you would see this as extra velocity.

Next on the short list would be the brass itself. Some brass requires you to drop your load up to 4 grains for the same chambering. Norma 300 Weatherby brass weighs 220 grains and RWS 300 Weatherby brass weighs 298 grains. Whichever brass you choose to use is up to you but your loads are for one brand of brass only. A safe load in Norma 300 Weatherby brass is a over pressure load in RWS brass by 4 grains.

I would also check your sizing of the brass. If you shrink it down to much it slaps against the chamber walls upon fiting and will give you a high pressure reading. Take one new case and load it down 5 grains and try it out. Gradually increase the charge on that very same case in 1% increments until you see pressure signs. In your example the increments would be 0.5 grains and you would use the same piece of brass because after the first firing it will better fit your chamber. Also on a new gun from a gunsmith make sure you thoroughly clean your barrel and dry your chamber very well. Gunsmiths tend to be under great amounts of pressure to get work out and from time to time will forget to clean a new barrel. You want the chamber dry because the liquid won't allow the brass to grab the chamber walls an you will get instant sticky bolt issues. A lot of experienced reloaders will lube the bodies of wildcat chamberings so they fireform better on the first shot.

Good Luck with your new rifle."

 

[AKShooter]

Going to try and get out at lunch tomorrow. This time with a chrono in hand. I have a few points to expand on.

Smith said he loaded a 140 to factory OAL, which is 2.825. No issues at all test firing, it was a reasonable amount of H1000 for load. My loaded rounds were measuring 2.910. My measurements to lands was 2.928 (average of about 10 measurements) I was not engaging into the lands at 2.910 but was close. I have some loads ranging from 50-56 grains, already know 54.5 grains is max, but OAL for these rounds is 2.860, so well away from lands. Just playing that card out. At about 52 I have another series that has had the neck shortened, again to chase that one.

At that point I'll have enough fire formed cases to load up too. So far have shot virgin brass.

One last new item, the chamber has been throated LONG for 180's, again, can't verify this until a chamber cast is made.

Lastly, I mentioned copper fouling, actually took a few treatments of wipeout to get all copper out. Noticed towards the end, was pulling only blue (copper) out of one land, just something I figured I'd add.

Smith is as confused as me, and has a standing offer to take it back to look at, certainly no ill feelings towards him, he has been great! Just trying to sort it out. Hope to have some range data tomorrow!!

 

[ar10ar15man]

if you know 54.4 is max for long rounds....WHY WOULD YOU GO TO 56 WITH SHORTER ROUNDS ??

 

[AKShooter]

I already have a pile of ammo to unload! If pressure holds true to past, or velocities put me close to factory velocities at the lower powder charges,,,I'm done,,, then simply unloading 55-56 Should have mentioned that, just figured better to have them, just in case being that close to the lands was the issue.

I simply figured the handloads used to test fire are my best info so far, in my head, I think maybe being that close to lands, adding the fact that I may be pushing shoulder out, I may be getting a "jamb" pressure. Just trying to chase all the tips I've been given. If I was to go out and buy some factory rounds, they would be 2.825. Just trying to get closer to factory

Hey, my bread and butter data collected is going to be from 50-54.0 grains no doubt.

What this thread is lacking is CHRONO DATA! Hope to fix that tomorrow

 

[AKShooter]

I was able to follow through with a range report! Dang cold day and my chrono went to low battery half-way through. We are suposed to get to the high 30's this weekend so I'll try and duplicate results.

To start, I really believe my OAL is my issue. I actually went all the way to the 56grains with zero pressure signs and no hard bolt lift

51.5 grains 2405fps
52.0 grains 2480fps
52.5 grains 2520fps
53.0 grains 2580fps

Thats were my chrono bit the dust, Nolser lists for their starting load 55.5grains at 2750fps

Went on to shoot 53.5,54.0,54.5,55.0,55.5 and 56.0 two rounds per charge

Zero pressure signs, primers were staring to flatten slightly, but I was comparing them to a 51.5 primer too.

Recoil, although kind of subjective, seemed lower too, even at the 56.0 vs the overpressure 54.5.

No brass on bolt head, I really do think I'm onto something, I hope. Going to get chrono back in order and reload another panel, and repeat the process with the same OAL. Again recording all velocities. Have 22 rounds through gun too, so on my way to getting it shot in

 

[AKShooter]

Dang fellas, Sure hope you guys are staying with me.....So I think I'm onto something, OAL. Got some decent feedback with reduced pressure, etc.

So I come home, take my fired rounds and run them through a redding neck sizer, used a .316 neck.

They will chamber, but they are tight the whole cycle, bolt does close but boy,,, not easy thats for sure.

Even used brass that was at the lowest charge fired, the 51.5.

I'm stumped and more than confused, I'm really at the point of shipping back to gunsmith, what am I missing? The brass fired showed signs of pressure will not rechamber either fired or head sized.

With being able to put 2 pieces of tape on a case and still chamber a round has me thinking I may have excess headspace? And thats messing up the show?

To the naked eye you can see the shoulder pushed out further than a virgin case,

I'm open to any thoughts