Tight throat or oversized bullet or ????

[mtang45]

I have been loading for a 338 Norma Mag for a couple of years. A few weeks ago I was at the range doing some random shooting and had 5 338 Lapua 250gr Scenars that I had loaded up with RL-25 just to see how the Scenars shot. 2 of the 5 would not chamber, I could not close the bolt. The others were a little stiff but the bolt closed. The 2 that didn't chamber I figured I had loaded a bit long and didn't think too much about it. The 3 that went in made a really nice 3 shot group. So I decided they deserved an OCW test.

Last night I was loading up some additional Scenars and I put one in the chamber and tried to close the bolt, no go. Again I figured I was long so I forced the bolt closed thinking that I would have rifling marks on the bullet but I would seat it further and could then measure base to ogive for a max length. When I removed the cartridge what I saw was not slight rifling dimples at the ogive but scrapes down the shank almost to the case mouth. Almost like the bullet was being forced through the throat. I measured the shank diameter and it measures .3380. I puled out some boxes of Sierra, Hornady and Berger and they ALL measure .3375. Now I know this is a mighty fine difference, but is it possible that the Scenars are oversized? Is my throat undersized? Never had an issue with any of the other brands.

Has anyone run into this kind of thing before?

 

[lrgoodger]

How's your runout? When you get a tight fitting bullet like that, the runout has to be near perfect so the bullet goes in straight. I've had bullets seated with a lot of tension and excessive runout refuse to chamber until I got the cartridge straight.

 

[Dusty Stevens]

Check your reamer print for trim length and check for a carbon ring

 

[Northridge]

I know you mentioned drag marks on bullets but another thing to check if brass has a few firings would be the loaded round neck diameter. Not sure if your bullets are seated beyond neck shoulder junction but in some applications buildup of donut will swell loaded neck diameter to the point that the back portion of neck comes into contact with chamber wall causing tight chambering, random tight chambering etc. How much neck tension do you run? In diagnosing issue try a sized piece of brass first in chamber with out firing pin in bolt then try again after loading. If you no the neck diameter of chamber loaded round should measure less than chamber.

 

[mtang45]

How's your runout? When you get a tight fitting bullet like that, the runout has to be near perfect so the bullet goes in straight. I've had bullets seated with a lot of tension and excessive runout refuse to chamber until I got the cartridge straight.

Runout is near perfect in the neighborhood of .001 at the ogive, I have certainly had much worse

Check your reamer print for trim length and check for a carbon ring

I have no idea what reamer was used; custom build by RWS. As far as a carbon ring, that could be a possibility. What would you recommend to remove?

 

[Northridge]

If your chamber nk diameter is not indicated you can measure a fired case, then add .001th to that. This will get you close.

 

[mtang45]

If your chamber nk diameter is not indicated you can measure a fired case, then add .001th to that. This will get you close.

Northridge, I should have mentioned this but it is new brass. Thanks for the suggestion of the donut developing on fired/resized brass. I can certainly see that being a problem.

 

[fguffey]

2 of the 5 would not chamber, I could not close the bolt.

I do not know what you are going to do, ME? If I had two loaded rounds that would not chamber and I had 3 loaded rounds that would chamber I would compare. I would compare the rounds that would not chamber with the rounds that would chamber. I have comparators and I have datums, most of my comparators are datum based. Everyone knows the bolt will close on a go-gage, few know how to determine 'by how much'. Everyone knows minimum length/full length ammo will chamber, they do not know by 'how much'.

F. Guffey

 

[hogpatrol]

Somebody please get the liquid refreshments.

 

[jlow]

As far as a carbon ring, that could be a possibility. What would you recommend to remove?

My understanding is this is pretty hard to do but perhaps it would be worthwhile to find someone with a borescope to check before doing anything heroic?

 

[dkhunt14]

My guess is that you had the bullets out to far and they hit. Some moved when you shut the bolt and others probably didn't move. If you would have checked the loaded length of those rounds you would know if the bullets moved or not. Also I believe the scratches are from carbon in the throat. That is a big case with slow burning powder and carbon is not hard to form. It could just be a little bit but that of a rough firecracked throat is usually what scratches the bullets. Matt

 

[fguffey]

dkhunt14, then there is that other problem, if the bullets were jammed into the rifling I would expect the bullet to be pulled when the case was extracted.

And as always, when seating bullets there is a chance the seating die is adjusted to low, some dies crimp and seat. I believe crimping bullets in bottle neck cases is a bad habit, there is a chance the case body/shoulder juncture can upset.

Simple solution, compare the loaded rounds that will chamber to the loaded rounds that will not chamber.

F. Guffey

 

[effendude]

Buy or make a Stoney Point Case gauge to measure distance to the lands. Buy a drill and tap if necessary to make one if Hornady doesn't make one for that cartridge. Everything is for sale and easy to find on the internet.

Scott

 

[dkhunt14]

F,guffey I always load into the lands and hardly ever pull a bullet. Even with a tight necked Dasher with very thin necks usually doesn't pull a bullet. I said he needs to measure the ones that chambered and compare to the ones that didn't. I still believe it is the seating depth. Big diameter bullets like in my 338 take a lot more bolt pressure to move them. You can tell by looking at the loaded round if they are crimped or not. If he loaded the rounds for years and never had a problem and now he tries a big bullet and they don't chamber it is usually seating depth. Matt

 

[lawrence97]

I have had what you described happen. All that was needed was a deep clean. Use some JB or iosso in the throat area. A short non rotating rod is best as you can spin it a few times in the throat area to knock the carbon loose.

 

[mtang45]

I appreciate all the input guys. I need to clarify some of the information; it cannot be COAL as defined by case head to ogive. Besides I know what pushing a bullet into the lands looks like. It looks like evenly spaced marks around the the ogive. This is even scuffing all around circumference of the shank.

I could seat these Scenars completely into the case so that the ogive was nearly at the case mouth and I would still get the "scuffing" around any exposed portion of the shank. I'm REALLY leaning toward the carbon ring and looking for a borescope to go in and look.

I'm going to take some pics shortly so everyone can see what this anomaly looks like.

 

[mtang45]

We have pictures! First is a side by side shot of the Lapua (left) and the Berger (right). The Lapua binds up and took considerable force to close the bolt. The Berger slides right in and the bolt closes like greased butter. See the scratches/marks around the ogive and shank on the Lapua?

Next are the shank diameter measurements Lapua .3375, Berger .3370. Only .0005 difference....but.

Now pics of the case length. Note the Lapua is .0055 longer but do not believe that's an issue.

AND last a close up of the Lapua

 

[/VH]

mtang,

I'm not saying it is but in your 2 pics that show the marks on the bullets; best I can tell, there appears to be land engraving marks. Is your barrel possibly a 5 or 6 groove? As that would be consistent with the spacing of what I see as possible land marks. If they sure enough are not land marks, then you may very well have a tight throat and I expect you've got some hard carbon in there as well. I guess a chamber casting could give you an idea of the freebore diameter.

 

[mtang45]

mtang,

I'm not saying it is but in your 2 pics that show the marks on the bullets; best I can tell, there appears to be land engraving marks. Is your barrel possibly a 5 or 6 groove? As that would be consistent with the spacing of what I see as possible land marks. If they sure enough are not land marks, then you may very well have a tight throat and I expect you've got some hard carbon in there as well. I guess a chamber casting could give you an idea of the freebore diameter.

VH/, You are correct it is a 6 groove. I can't see the markings you are seeing, but my eyes are not what they used to be. It looks like solid contact all the way around to me.

Thanks for the input. If I can get pics with a borescope soon I will post them.

 

[gotcha]

Not to be a party pooper but a neck & free-bore clogged with hard powder fouling won't give you an accurate chamber cast. Try some JB's or comparable 1st....... Remember this clearance problem didn't exist previously. Some free-bores are ridiculously close to bullet diameters. Hard powder fouling in F/B or neck will further reduce those diameters. Twirl an undersized bronze bore brush coated w/ JB's in the chamber neck to get at the carbon located at the "step" from neck to free-bore. Got this tip here at the forum and worked very well on a tight free-bored .223 I have. Good luck !!