So I posted awhile back on sooted up necks, worse than normal, on my 300 RUM. I also noticed I was experiencing pressure long before most others on similar powder and bullet grains. At 90.5 I was seeing high pressures on the case heads. Although I was still seeing over 3120 fps with the 215 I knew there was much more available, being I'm running a 29" Brux. I have my reamer that was used, a 343 nk 108 fb. I measure both brass types, Rem and nosler. They are at 341-342 OD loaded!! The neck wall is around .0155. Guess I have to turn some necks! Thinking of taking them down to .012. What do you guys say? It's more of a target rig than hunting but still used
Duhh! Figured out the pressure problem
- Thread starter Dshooter
- Start date
First off I think your freebore id too short for the 215 bullet. When the freebore is short it uses up capacity of the case. On my 300 I use a .210 freebore and the bullets pressure ring is just barely ahead of the neck shoulder junction. The farther out in the case you move the bullet usually means less pressure. I would throat the gun out so the pressure ring is in front of the neck shoulder junction. If you turn the cases to .003 clearance you have enough. In other words you want .340 minimum loaded. A .016 neck wall thickness should be ok. In hunting guns I like .004 clearance which would be .0155. I think you need to check your measuring. How are you measuring the case neck thickness? It should be done with a ball mike and checked at different places around the case. It should also be checked from front of neck to the shoulder. Matt
Thanks dk. I have a mitutoyo tube mic and it has the vernier scale on it. I do check necks in 4 quadrants, this is how I came up with the avg of .0155. This is somewhat standard equip in my line of work. Believe me, there is more than enough FB to run the 215.... My loaded round is .050 off the lands and the OAL is 3.920. I thought that maybe it was a misprint by ptg but it's not. I checked that as well. If I go to .012 wall on the cases, that'll take the loaded Neck OD to around .338-.339. That'll give me .004-.005 clearance....
A tube mike isn't as good as a ball mike. The one that K&M sells has the spindle ground so you can even get close to the shoulders. If you subtract the bullet diameter from the neck diameter of the gun .343 minus 3 thousandths for clearance = .340 minus .308= .032 divided by 2 which is .016 wall. You can give it another thousandths clearance which is .0155 wall. Is the pressure ring of the bullet ahead of the neck shoulder junction? Matt
Matt, I will attach some pics for you. I understand the spindle is nt ground on this mic but it is the one that this site actually promotes. I do understand the mathematical route to get the answer but it is not working out that way. As for pressure ring, those to my understanding, are only on flat base bullets. I checked, just now, several bullets out of the berger box with a mic and they measure .308 the whole bearing surface. As for seating depth, I was off. My OAL is 3.825. Only about .060 of bearing surface and the boat tail is south of the junction. I noticed on my fired cases, the ID is a snug .308 and the OD is just shy of the .343 due to spring back. Again loaded OD is .342 and neck wall is .0155
No...I do appreciate the help! I've been beating my head to figure this thing out. There is about .060 or so of the bearing surface south of the junction. Only reason I'm not so sure that is the problem, is with 90.5 gr of powder you can shake the case and hear it rattling around. Tons of space left in the case. Just for grins I checked, I can fit 97gr of Retumbo in there at my current seating depth before it starts to crunch. I'm just wondering why the math doesn't work out like it should. I've been measuring everything and I'm well within .0005 with the equip I have but overall product is what it is. Hence the reason I was thinking of turning to get the OD where it should be in a loaded case
I can't get the pics uploaded on here...says the file size is too big. I can email them if you'd like to see. I do appreciate the help and have been checking things again as we chat. I was thinking there isn't enough space between the wall and case OD to cleanly release the bullet therefore building excess chamber pressure??
Most of the Berger VLD and hybrid bullets have a pressure ring. I believe you may not be getting the necks turned to the right dimension all the way to the shoulder. Then when the bullet gets in the case it is too big there and pinching the bullet. I like my junction of where the bullet body meets the boat tail to be at least 30 thousandths in front of the neck. In my Dasher the pressure ring is out in the middle of the neck. Its throated at .155 freebore. That is how I get 3050 with 105 and no pressure. Email the pictures to me. Matt
Thanks for the input guys. So even being with .001 clearance is enough, then consider spring back, my FIRED cases have an ID of .307. That's still fine? I thought I read on here in the main pages, .002-.003 for comp guns and .004-.005 for hunting rigs? Maybe I misread. I'll have to check.
On the seating issue, SAAMI is 3.60. I'm at 3.82 and yes with a lot longer bullet I understand. I'm loading between 90.5 in nosler brass and 92.0 in Remmy brass with a ton of room left in the case. With the 215 hybrid, I can go to 97 gr of Retumbo w/o compression at the current seating depth. Technically, I've tested this 3x now, 97.4 is when it initially starts to get tight. I will never need that much powder nor would this chamber allow that much pressure. I'm seeing 3125-3136 fps. That is also where I start to see ejector marks. I just didn't like the heavy sooting on the necks and with a 29" barrel, not that I would need them to be pushed that hard, but I should be able to see high 3100s before pressure. I will consult QL again also....
On the seating issue, SAAMI is 3.60. I'm at 3.82 and yes with a lot longer bullet I understand. I'm loading between 90.5 in nosler brass and 92.0 in Remmy brass with a ton of room left in the case. With the 215 hybrid, I can go to 97 gr of Retumbo w/o compression at the current seating depth. Technically, I've tested this 3x now, 97.4 is when it initially starts to get tight. I will never need that much powder nor would this chamber allow that much pressure. I'm seeing 3125-3136 fps. That is also where I start to see ejector marks. I just didn't like the heavy sooting on the necks and with a 29" barrel, not that I would need them to be pushed that hard, but I should be able to see high 3100s before pressure. I will consult QL again also....
W/regard to pressures, ANY amount of neck clearance is enough. When a neck has expanded only .000000001 over bullet diameter, the bullet is completely free.Dshooter said:
But then, you have to actually have that clearance with no generalizations about.
If you're seated into donut, your clearance could be gone, and effective neck tension could be considerably higher.
People choose clearances they can manage given other abstracts in the mix. For instance, where you have a bunch of runout, or dirty ammo/chamber, it may be beneficial to relieve your chambered pressure points with more clearance.
I just think you should know that neck clearance in itself, provided there is any, is not causing a pressure problem.
Also, lower clearance doesn't lead to neck sooting. You get this with excess clearance, or excess trimming from chamber end, or a reduced pressure load.
Maybe I missed it. What is your pressure 'problem'?
Mike, I appreciate your input. I will say that I politely disagree given specific circumstances. If the neck expands just .00001(0ne one hundred thousandths) over the bullet diameter, in a set temperature the entire time of expansion, then yes you would be correct. Given the fact of pressure friction and heat, the brass does expand do to the heat. Therefore would not be releasing the bullet cleanly. Due to heat, all metal expands, even in thickness. Therefore a set amount of clearance IS needed to make up for this and other factors. And considering the fact that this is a magnum cartridge burning X amount of powder, IM sure there is a fair amount of heat created. How much clearance needed is the real question. I reread the article on this site and its recommended .0015 radial clearance or .003 total for competition guns. I realize some guys run even down to .002. But .001 I would think is a bit tight and possibly creating drag on the bullet as it leaves the neck.
More clearance than required is recommended, and I also recommend no tighter than you can manage. Over time people have settled to what works well for them.
I'm just saying that where you have neck clearance, any actual amount, then that neck clearance is not causing a pressure problem.
Apparently you're convinced otherwise. You started this thread that way. But there is no reason for other folks to convince themselves of the same -from your notion alone.
I personally manage a fitted chamber with no more than 1thou total clearance for necks, and it does not cause any problem at all. That is, there is no more pressure as fitted than with larger to excessive neck clearances, and there never was a reason to think there would be.
This chamber also snaps back to -1thou, ready to reload, without sizing. I do not have & seat into donuts though. Doesn't makes sense for anyone to do that.
I'm just saying that where you have neck clearance, any actual amount, then that neck clearance is not causing a pressure problem.
Apparently you're convinced otherwise. You started this thread that way. But there is no reason for other folks to convince themselves of the same -from your notion alone.
I personally manage a fitted chamber with no more than 1thou total clearance for necks, and it does not cause any problem at all. That is, there is no more pressure as fitted than with larger to excessive neck clearances, and there never was a reason to think there would be.
This chamber also snaps back to -1thou, ready to reload, without sizing. I do not have & seat into donuts though. Doesn't makes sense for anyone to do that.
Ok...I respect your advice. My opinion, and only that, was by turning necks I would create a thinner wall therefore making it able to open quicker and seal the chamber better. Just a hunch is all. I would think that thinner brass moves a little faster than thicker brass. Hence, fixing the sooting problem. My actual question in the beginning of this thread was, is .012 wall ok and .004 clearance better for my situation. Just not in those exact words, sorry
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