Got a custom 300 PRC barrel built for my AXMC. finally got around to taking it out today to shoot. it was extremely tight when trying to chamber a round. I hard to push down hard to get the bolt down. I had a well known experienced ELR shooter look at it, and we put two rounds through it but have some interesting marks on the brass. doesnt seem unsafe to shoot, but i think i will have accuracy/velocity problems. When the barrel is out the round seems like it fits in very nice. Any guesses on the problem? I plan on taking it to a smith this week.
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Gunsmithing AXMC barrel smiths...300 prc problem
- Thread starter solvovir
- Start date
Try this: open the bolt and clip a round onto the bolt face, then move the bolt into battery like you normally would. Do this with the safety in the middle position so you are not fighting the cocking action.
Let us know how it feels then.
That will prove or disprove the theory of extractor grabbing, for the most part.
Outside of that you could try sizing a piece of brass just to see if that makes a difference.
Let us know how it feels then.
That will prove or disprove the theory of extractor grabbing, for the most part.
Outside of that you could try sizing a piece of brass just to see if that makes a difference.
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Color up a tight fitting piece of brass (Sharpie), close the bolt on it and then look for the witness mark on the brass after extraction. This could tell you if it is minimum headspaced and you are just dealing with wide variances in hornady brass. If you are using factory loads , color the bullet too; if there is a witness mark on the bullet, then you have another problem.
I only shoot factory ammo. I do not reload. every round of factory hornady 225 felt the same. I can get the bolt down, but it almost takes two hands. seems like it is extracting fine.
these witness marks?
these witness marks?
Wish we could help there by watching the video but it doesn’t really mean much, unfortunately.
Top two images: nothing to be alarmed about. It’s simply the gas coming around the necks of the case. What you wouldn’t want to see is that gas going down the shoulder.
Bottom image: That just looks like a feed ramp mark, or a random blemish from the factory. It’s not radial so it’s not from caming over.
You should try the suggestions that I made, as well as f>b25 and let us know the results. Got to start somewhere! I doubt the OAL on factory ammo is too long but you never know.
Top two images: nothing to be alarmed about. It’s simply the gas coming around the necks of the case. What you wouldn’t want to see is that gas going down the shoulder.
Bottom image: That just looks like a feed ramp mark, or a random blemish from the factory. It’s not radial so it’s not from caming over.
You should try the suggestions that I made, as well as f>b25 and let us know the results. Got to start somewhere! I doubt the OAL on factory ammo is too long but you never know.
Sounds like headspace is a bit tight for the ammo your using.
pretty rare with factory ammo but certainly not impossible.
jamming bullets is a good amount easier than jamming shoulders.
pretty rare with factory ammo but certainly not impossible.
jamming bullets is a good amount easier than jamming shoulders.
It’s probably just headspace. Prior to chambering my barrel, I measured a bunch of virgin PRC brass. Every single piece was longer than the go gauge by .0015-.002. In a minimum chamber, they just don’t fit. I chambered my barrel accordingly.
If you have a depth mic, measure from the face of the action to the bolt face. Now measure the length of your tenon(should be 1.499-1.5”), and subtract that from the face to bolt face measurement. That figure will be the max protrusion your case can stick out of the barrel. Then chamber a fresh round in the uninstalled barrel and measure for protrusion. If any of this is confusing to you, don’t bother with it. Let the gunsmith who did the barrel fix it.
If you have a depth mic, measure from the face of the action to the bolt face. Now measure the length of your tenon(should be 1.499-1.5”), and subtract that from the face to bolt face measurement. That figure will be the max protrusion your case can stick out of the barrel. Then chamber a fresh round in the uninstalled barrel and measure for protrusion. If any of this is confusing to you, don’t bother with it. Let the gunsmith who did the barrel fix it.
That sucks that new PRC brass is longer than a go gauge.
.015-..002 is plenty to make things tough on a minimum chamber.
I would be having a few words if I got short chambered (that tight to absolute minimum) considering you can’t get the brass from anyone else right now unless you want to make it from 375 Ruger.... or 8x68S. I mean really, the user is going to be using Hornady brass!
Most new brass I have ever bought needed to be sized first. I think they leave it long so people can size them for their chamber. If they were sized to SAAMI spec and you had a longer chamber it could cause problems.
Looks like normal axmc lfp cratering to me....but def wanna get that bolt bushed
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Yeah, pretty normal. You have to judge by the radius. Still round, not flat ?
While I agree that virgin brass needs to be sized, that’s mostly because of the necks, not headspace. I can’t recall ever running into virgin brass that was long. Certainly it happens, but usually it’s one or two thou short, or much shorter.
I don’t have any more virgin to measure, but I measured some 225 eld ammo and 212 precision hunter ammo. All was at zero to .002 short compared to my go gauge.
Tell me more about this...
I was aware of the bolt bushing with the older AIATs and AX308 (large firing pin vs small firing pin) but i was unaware it could be needed with the AXMCs. I purchased my axmc this year when brownells put them on sale, thd serial makes it a 17' build date.
Note the Sharpie mark. When the shoulder is marked, chamber and look for places where the ink is removed (witness marks). You may have to do more than the shoulder, but I would start there
Attachments
Sizing new brass necks?
Yes
Sizing new brass shoulders?
Hell no.
lots of factory rifles have long chambers.
brass stretching .005 or more is not optimal but not rare.
Unless you’re reloading and want maximum brass life it’s a non issue.
Ammo loads, deer drops.
I can’t ever remember factory loads or brass that was greater than a go gauge, tightest ever was my current 7 saum barrel.
that brass is like half a thousandths less or equal the go gauge.
I feel if OP’s rifle closes on a go gauge(and it’s correct)and factory ammo doesn’t load or is stupid tight it’s 100% the ammunition at fault.
It looks tight on the shoulder., but from the pic I don't think it's conclusive. The neck mark is likely just feed ramp contact under the pressure of the ejector, not an issue (cf AIAW's comment) You could unscrew your barrel a 1/4 turn or less and then try to chamber. If there is no camming pressure, then it confirms you have a chamber that doesn't like your brass. It is not necessarily your smith's fault, but you'll likely find satisfaction with him before you do with hornady. Keep us posted-good luck
I did this and the bolts drops very easy. cycled a full mag a few times and apart from some of the ammo not feeding well from the 300wm mags, dropping and lifting the bolt was smooth and easy. every round extracted fine.
Update to this.
I took it to the guys over at Alamo Precision (they did not make the barrel.) They stuck a gauge in there, headspace just a hair too short. They are going to add .001 or .002 and it should chamber just fine.
I took it to the guys over at Alamo Precision (they did not make the barrel.) They stuck a gauge in there, headspace just a hair too short. They are going to add .001 or .002 and it should chamber just fine.
Its always best to have your gunsmith build the barrel to your AXMC instead of buying it off the shelf. The large actions dont headspace all the same like they say they do
Learned this the hard way. At least if they are making switch barrels if the smith has a similar chassis they can test the barrel in that should help eliminate potential issues.
I don’t think this is necessarily true. OP has one bad barrel. How many AXMC users just order a barrel and run it? I can speak for at least 3 rifles and 7 barrels without issue.
A vital component of the pre-fit barrel ideology is action headspace consistency.........
Picked up my barrel today. I believe it is good to go. Havent test fired it yet, but with the headspace go gauge the bolt drops nicely (before you would have to push really hard to get it down) and with the no go gauge the bolt wont drop.
All of your AXMC la rifles and seven barrels are exactly headspaced the same and timed to 12 or 6 oclock?
Mine are all over, except the ones i had a gunsmith build off the reciever/bolt
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My one rifle and 4 barrels all shoot fine. Didn’t check headspace on any of them. Didn’t have any issues with primers. Which part are you timing?
I think it is important to recall that headspace gauges can vary between manufacturers, so the smith is not necessarily to blame. A person could gently point out that the rounds did chamber and safely fire. Nevertheless, it does not fall to the man paying the bills to know what the man doing the work should know; don't headspace to minimum specs, especially when using hornady. Go plus .003-.005 usually accounts for hornady brass as well as differences in gauges. Solvovir, I hope you burn up the new barrel and enjoy: contact Dave Tooley next time to avoid this experience/thread.
They will shoot fine even if they are long in the tooth .
By timing I meant where is the barrel pointing.
100% this. We rely on the manufacturers of custom actions to ensure their tolerances and QC processes are on point. There are only about 10 actions currently on the US market which hold consistent enough tolerances.
The barrel points down range. I couldn’t possibly care what degree anything is at.
Just some random thoughts. Your chamber was a bit short at a different smith's shop. The question is , How short? Gages do vary slightly and when you get steel to steel contact even a few tenths difference will seem way out of spec. I'm guilty of putting in min chambers even though I know they may make the phone ring. As has been suggested it should be min +.003". to CYA
Your problem may have nothing to do with HS. I see this a couple of times a year. The radius at the shoulder-neck junction of the cartridge case doesn't match the radius on the reamer. Reamers are not all identical clones. Same goes for any manufactures cartridge case, which I'm sure vary much more than the reamers. Most of the time this is just annoying and goes away on the first firing. Another thing with Hornady brass is the way they trim it to length. I have seen the case mouth flared to the point of having an interference fit in the chamber. If I start with new brass I always run an expander through the neck and chamfer inside and out. Then I'm off and running.
Your problem may have nothing to do with HS. I see this a couple of times a year. The radius at the shoulder-neck junction of the cartridge case doesn't match the radius on the reamer. Reamers are not all identical clones. Same goes for any manufactures cartridge case, which I'm sure vary much more than the reamers. Most of the time this is just annoying and goes away on the first firing. Another thing with Hornady brass is the way they trim it to length. I have seen the case mouth flared to the point of having an interference fit in the chamber. If I start with new brass I always run an expander through the neck and chamfer inside and out. Then I'm off and running.
f>b25 called it when he said it was too tight on the shoulder. Thats the same thing Alamo said when i took it to them. Before they would fix it they said they wanted to see the original smiths reamer print. So I got a copy of the original smiths reamer print, Alamo said it was the same as theirs, and I think they hand reamed it to fix it. As mentioned above with the headspace go gauge the bolt drops nicely, with the no go gauge the bolt wont drop.
And not only headspace but thread specs too. That's why pre-fit barrels typically have a thread fit that top tier builders would be ashamed of...…...but they seem to shoot well...….or at least well enough to justify their existence. I "grew up" on the cut threads to part mentality (at least when I knew part interchangeability is a non-issue).......I still push this idea for best accuracy possible along with headspace of <+.001.......basically making a "matched" barreled action........regardless of maker and their tolerances.
Having said that, I have seen my pre-fits shoot unbelieveably well...….but I always wonder how much better they would shoot with a little tighter fit everywhere.
Just my $.02
Ern
In my experience tighter specs, IE thread fit and dead nuts min chambers mean nothing on the target. I spent the first 10 years of my career complicating things in the short range BR world. The next 10 figuring out what really mattered in the 1K BR world and the last 15 enjoying work.
Mr. Tooley,
Thanks for sharing your experience, it is much appreciated. Your experience has reflected my short experience with my own pre-fit barrel on target accuracy. Perhaps "tightening" them up would not have made a noticeable difference...….unfortunately we will never know...….as ALL barrels are different.
Ern
Thanks for sharing your experience, it is much appreciated. Your experience has reflected my short experience with my own pre-fit barrel on target accuracy. Perhaps "tightening" them up would not have made a noticeable difference...….unfortunately we will never know...….as ALL barrels are different.
Ern
I agree with Dave, tight threads mean nothing. A quality machine, tools, inserts, spending time on what actually matters, a really good setup, and a little bit of knowledge equal good shooting barrels. There isn't any magic too it like so many people seem to think. Its extremely basic machining processes.
Wish I noticed this thread a few months ago. I have the same issue with my AXMC 300 PRC barrel. Did you get yours through Bugholes? Any way, I shot the entire Nightforce ELR match with no accuracy or pressure issues but my right palm was sore from hammering that bold down. Mine is a few thousandths short in the chamber as well. Going to have my local smith clean it up before next year's match.
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