Gunsmithing Chamber Chamfer for improved feeding with minimal body taper cartridges

[Clint E.]

Guys,
I was wondering if anyone had any experience with changing the size of chamfer on a chamber to improve feeding of cartridges with minimal body taper i.e. Creedmoor, BR etc.?
I was looking at my AIAX 308 barrel and noticed that it has a substantial chamfer at the back of the chamber. When compared to my 6mm Creedmoor AIAX barrel you can see that it is larger. When compared to a typical Remington setup the chamfer on the AI's are both substantially larger.

I noticed that if I chamber a round with the AIAX 6mm barrel and move the bolt very slow the round will pop up as it leaves the lips of the magazine and then bind slightly afterwards as the bolt pushes the cartridge into the chamber, you then either have to take the forward pressure off the bolt the allow the case to align with the chamber or force it in. With the 308 AIAX barrel this happens but it is almost imperceptible. I think this is because of the larger chamfer on the 308 barrel, and the additional taper of the 308 case. Both cartridges feed fine when running the bolt quickly but the 308 is smoother.

Ultimately the reason I ask is because I have been trouble shooting a feeding problem with a R700 clone action and I think this may be one of the reasons it doesn't feed quite as nicely as my AI does. If you look at the typical chamfer on a R700 chamber it is non existent compare to the AI barrels.

Just looking for thoughts and experiences.

AIAX 308 Chamber

AIAX 6mm Creedmoor chamber

Remington 700

 

[_Windrider_]

I usually like an 11 degree chamfer on the R700. I’ve done as high as 30 but have had good success at 11. On that R700 chamber, it looks a little shallow. I think you are on the correct path.

 

[Rubicon Precision]

I usually like an 11 degree chamfer on the R700. I’ve done as high as 30 but have had good success at 11. On that R700 chamber, it looks a little shallow. I think you are on the correct path.

That 700 style tenon's chamfer to chamber is somewhere around .020-.025" and at 45°. I'm guessing that picture was taken early 2015. I may know the guy that machined it...

With a recessed bolt nose, the chamfer isn't as important as with a flat breech face as the counterbore pretty much guides the nose in the right direction. I still like to avoid sharp edges, The main thing you want to stay away from is having too much unsupported case outside the chamber.

 

[Supersubes]

My aw 308 barrel looks a lot like your .308 barrel. The few I bought from mile high look like your 6mm barrel. When I started doing my own, I copied the mile high barrels. My tempest tenon print calls for 50 degrees and the OD of the bevel at .574”. They all seem to feed the same for me.

 

[_Windrider_]

With a recessed bolt nose, the chamfer isn't as important as with a flat breech face as the counterbore pretty much guides the nose in the right direction. I still like to avoid sharp edges, The main thing you want to stay away from is having too much unsupported case outside the chamber.

True. I guess that’s why put so much time into trying the R700 actions boots and chamber. In this case it could be that the chamber and bolt aren’t in perfect alignment.

 

[Clint E.]

The main thing you want to stay away from is having too much unsupported case outside the chamber.

So with that being said is it variable to increase size of chamfer on a barrel that has already been chambered? OR will this leave too much of the case unsupported?

My aw 308 barrel looks a lot like your .308 barrel. The few I bought from mile high look like your 6mm barrel. When I started doing my own, I copied the mile high barrels. My tempest tenon print calls for 50 degrees and the OD of the bevel at .574”. They all seem to feed the same for me.

The difference in feeding is hard to notice when running the bolt normally, it is really just when you go really slow.

 

[Supersubes]

I wouldn’t worry about it then. I think your 6mm barrel looks about perfect personally. A good portion of the bottom of the case is solid brass. You can measure it with the depth function on you caliper and then transfer that to the outside of the case to give you an idea where the floor is. There should be some safety margin there though so the case wall can’t possibly blow out.

Edit: The remclone barrel could use some more chamfer imo, but make sure that’s the cause of your issue before you pay for the fix.

 

[Xander3Zero]

Check with whomever chambered the barrel before you think about doing anything. Like others said, the important thing is to not have too much unsupported case.

I had some feeding issues with a 223 chamber; at my request my gunsmith slightly increased the chamfer size (only enough to still maintain a safe amount of supported case), and he reported that it made no noticeable increase in feeding reliability.

 

[Clint E.]

Both of the AI barrels feed fine it is more the R700 clone that I am worried about. It binds more often than not if you causally push the bolt forward, running it fast it doesn't come to a complete stop but I feel it is just not as smooth as it could be. I have attached a couple more pics below that show the position that it binds and the corresponding scuff on the case.

I should also mention that the previous pic of the R700 chamber is not actually this particular rifle but it is very close.

 

[_Windrider_]

If this 700 hasn’t been trued I would suggest having that done. What is likely, is the barrel and chamber aren’t in perfect alignment with the bolt. Couple thou here and a couple thou there make a big difference. SAC or area 419 will take good care of it.

 

[Geno C.]

I have played with the this quite a bit with 223ai trying to get them feeding smooth. I always had a mark like you show on your case. I knocked down all the edges on the bolt recess and the chamber. While it did help it never fixed it. The biggest difference was made my messing with the way the mag release the round. I trashed a couple mags going too far but finally got it right. If the mag releases the round too soo, the case isn't far enough in the chamber and it jumps up past the bolt face. Too late and you get the marks like you have.

 

[Shooter71]

The issue is not the chamfer. The nose of the bullet is contacting the top of the chamber while the case is still constrained by the feed lips, wedging it into the chamfer. Long bullets seated way out and straight cylinder shaped cartridges make it worse. You need to mess with the magazine and when it releases. Don’t sweat the chamber.

 

[Rubicon Precision]

Both of the AI barrels feed fine it is more the R700 clone that I am worried about. It binds more often than not if you causally push the bolt forward, running it fast it doesn't come to a complete stop but I feel it is just not as smooth as it could be. I have attached a couple more pics below that show the position that it binds and the corresponding scuff on the case.

I should also mention that the previous pic of the R700 chamber is not actually this particular rifle but it is very close.



View attachment 6928522View attachment 6928521View attachment 6928520

I’m leaning toward that being a magazine issue, not a chamfer/radius issue.

In AIs I do a .040”-.045” deep chamfer at 45* (90* included angle) because that’s pretty close to the OEM barrels I’ve seen. On Big Horns and other non-recessed bolt nose barrels, I do a .040-.045 deep, 60* (120* included) chamfer. On recessed bolt nose barrels, I do a .020” 45* chamfer from the chamber to counterbore and .030” 45* chamfer counterbore to barrel end. I haven’t heard anybody complain about feeding issues or brass being scored from this.

K

 

[Clint E.]

The cartridge is well out of the magazine when it binds. Here is a video of it in action, the video is cut a bit short but basically right when the video stops is where it binds.

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[Shooter71]

Draw a sharpie ring around the case where the scuff mark is and slowly advance it until it touches the chamfer. Probably about where the pop happens. Are you full length sizing? You probably already did but pull the pin assembly if it’s a loaded round.

 

[Clint E.]

Draw a sharpie ring around the case where the scuff mark is and slowly advance it until it touches the chamfer. Probably about where the pop happens. Are you full length sizing? You probably already did but pull the pin assembly if it’s a loaded round.

So I played with it some more tonight, where the pop happens the cartridge is no where near the scuff mark. When the pop from the magazine happens the tip of the bullet is just entering the chamber. I am full length sizing.

It's not a huge deal, just not as good as I think it could be, I will probably end up shooting this barrel out and then trying a bit more chamfer on the next one.

Thanks for all your help guys!

 

[cwinston]

This may be totally off the wall, but in your video and pic #3 it looks like the back end of the case may be getting caught under the edge of the ejector plunger. You may want to try removing the ejector plunger from the bolt and see if the problem still persists.

 

[Geno C.]

Or adjust the mags to release the round later and see if that helps. You can see it's jumping above the bolt face quite a bit because there isn't enough case on the chamber when it gets free of the mag.

Just something else to try

 

[morganlamprecht]

This may be totally off the wall, but in your video and pic #3 it looks like the back end of the case may be getting caught under the edge of the ejector plunger. You may want to try removing the ejector plunger from the bolt and see if the problem still persists.

this^^

then look at your AI ejector plunger and grind the r700 ejector to match its shape and position

 

[_Windrider_]

this^^

then look at your AI ejector plunger and grind the r700 ejector to match its shape and position

Even better put a sako ejector on it

 

[Clint E.]

This may be totally off the wall, but in your video and pic #3 it looks like the back end of the case may be getting caught under the edge of the ejector plunger. You may want to try removing the ejector plunger from the bolt and see if the problem still persists.

this^^

then look at your AI ejector plunger and grind the r700 ejector to match its shape and position

I think you guys are onto something, I looked closer tonight and it's hard to tell but it appears that the rim of the case might be catching the plunger ever so slightly. I don't have the means to remove the plunger, but once I get tooled up I will try it and report back.

Thanks again for all of the help!

 

[baldie]

Its a common fault on ejectors with no radius.

I found this problem many years ago. The case appears to be 7/8 the in, and hangs up. With a shadow of a doubt....its the ejector.

I remove them and machine a radius on the end in a collet, but you can simply do it, by gripping the ejector in a drill, and taking some off with a file, and then emery.

You really cannot do this wrong. I make them dome shaped.

 

[flatland1]

I'm having the same issue with a couple of M700 actions I bought w/o bolts, then used PTG custom bolts with mini-16 extractors. The 6XC rounds pop-up just like the 6CM rounds in the video, and bind a bit when trying to run the bolt quickly. All it takes to get them to feed on in after that is to release the forward pressure on the bolt handle, they slide right on in after that. Only in these two rifles, it happens when you're running the bolt fast, as you would in a PRS-style match. I bought factory ejector plungers, springs, & retainer pins from Brownells for these two bolts - wonder if shortening the ejector plunger would work better than putting a radius on them? Or would it work better to grind an angle or radius only on the bottom side of the plungers, where the case contacts it after popping up out of the mag?

 

[morganlamprecht]

I shortened (level with the lower edge of the inner bevel of the bolt face) and put a radius on mine...haven’t had an issue since...just putting a radius on the plunger didn’t fix mine completely

 

[flatland1]

You guys are a treasure chest of good info! Just came in from test-firing my M700 in 6XC after shortening the ejector plunger .023" & putting a bevel/radius on the edge. Don't have a clue whether PTG supplies plungers of the correct length & with a radius or not. I bought the bolt bodies from them, along with complete striker assemblies, & mini-16 extractor kits, but since they were going into bare receivers, with no trigger or sear pins, nor bolt stop & spring, I bought all those factory Remington parts from Brownells, getting the ejector plunger, spring, & retainer pins for the bolts from them at the same time.

Whatever, mine fed much more smoothly than it'd ever done before - the only thing that worried me was that ejection seemed a little anemic at first - figured I'd gone too far while shortening the plunger. But after I'd run a 5rd mag through it, I then ran a 10rd mag full, and the ejection was perfect, We're GTG...

Actually, having worked with several Howa actions, I should've remembered the radiused ejector plungers that they use. They're not just radiused, but are actually a dome-shape, with no flat surface at all. And, the length is considerably short of the front edge of the bolt nose. Next Remington ejector I work with will get the nose rounded completely, then we'll see how that works.

 

[Clint E.]

Thanks so much guys!! the issue is now resolved!!

I shortened (level with the lower edge of the inner bevel of the bolt face) and put a radius on mine...haven’t had an issue since...just putting a radius on the plunger didn’t fix mine completely

I did this ^^^^^ by using a drill and a file. Pic below shows my modified plunger on the left vs. my factory AI on the right.