Can Undersizing Cause Tight Bolt

[wholman]

If your not getting ejecter marks on your case push shoulder back till
you don't have case swipe.

 

[Ccrider]

If your not getting ejecter marks on your case push shoulder back till
you don't have case swipe.

No ejector marks after firing. I have been watching closely. What is “case swipe.”

 

[243winxb]

Case swipe is when the case head is in hard contact with the bolt face. Then the bolt is opened, rotated. More noticeable when bass has flowed into the ejector hole.

I think this is more an AR rifle problem? The hot loaded round is still under pressure when the bolt rotates .

 

[jaybray]

A hard bolt open is a sign of excessive pressure in many cases. Make sure the chamber and ammo are clean. Moisture or oil can cause this problem. Try backing off .5 grains of powder.

I had pressure problems like crazy in my 6br for quite some time and couldn't figure it out. Tried backing the powder charge down to the minimal starting load and still had pressure problems. I even sent the rifle back to the gunsmith to have him check things over thinking he had made some sort of mistake chambering it. He made no mistakes at all. It turned out that I had failed to clean my cases properly after sizing and lube had built up in the chamber causing me horrid pressure problems. Finally thanks to members on this forum I cleaned my cases properly, swabbed the chamber with a bore mop soaked in brake cleaner then dried it out bone dry and the pressure problems were gone. I was inexperienced at the time and thanks to this forum I got it figured out.

 

[mikeeg02]

I took the firing pin out and still had that soft pressure sizing down to .002. At .0035 there is no resistance.

I think you'll find that's your answer. I had a similar experience this summer and took me a few 70 round matches before I correlated the slight pressure on bolt close to getting bolt lift. I even backed off the load .5 grains and it still did it until I made the correlation between slight pressure on close and bolt lift.

I go just enough to not have any feeling on close. I would not go passed that. Too far and you risk not putting enough energy into the primer to set it off.

Since I hadn't been annealing the die would need adjusted almost every firing until it settled. Then it was pretty consistent. I think annealing would allow you to pretty much set your die and forget it.

Also, you may find that you have to adjust your load some to match how much pressure goes into sizing your brass vs where your die was set before.

 

[boltfluter]

I would bet you are not sizing the base of the case enough. As a test you could take a brand new case and fire it with your load and see how it extracts. If it comes out fine you need a tighter die at the base. Usually takes several firings to fully form the case /base dimensions. A .308 die sizes the base very nicely if you have one laying around. Good luck!

Paul

 

[LCazador]

I think you have cases that have oversize head dimensions. Basically the case is head spacing on the head and not the shoulder. Pushing the shoulder back is just aggravating the dimensions but yes it will make the case fit the chamber. I would try a few new cases and see if this changes. Make a note of the head dimension on your new brass and then check the once fired brass head dimension. You should have less than .001" expansion. Use a moderate load when fireforming. BTW I use 31.8 gr. of Varget with a 95g Sierra MK. and that's not anywhere near max in my barrel. Lapua brass neck turned.

 

[mikeeg02]

31.8 of varget in a straight 6br ?!

 

[Alex Wheeler]

Diameter does not give heavy bolt lift, length does. Diameter will give sticky extraction. If your comparator is measuring the right place on the shoulder you can usually bump the case .002" and be good, in the video I purposely used a combo that was not measuring out perfectly to make the point. I have found a lot of guys are using different comparators that measure a poor spot on the shoulder like right at the body junction or the neck/shoulder junction. I like to see them measure mid shoulder. The best is a bump gauge made with the chamber reamer. If your using the bump tool that comes with a Harrell's die, toss it. I personally like a little more bump, but if you like a zero clearance fit where the bolt falls half way thats fine. Bump as much as you like. Excessive bump will hide pressure because your taking thrust off the bolt face. You probably are seeing pressure.

 

[LRPV]

Diameter does not give heavy bolt lift, length does. Diameter will give sticky extraction. If your comparator is measuring the right place on the shoulder you can usually bump the case .002" and be good, in the video I purposely used a combo that was not measuring out perfectly to make the point. I have found a lot of guys are using different comparators that measure a poor spot on the shoulder like right at the body junction or the neck/shoulder junction. I like to see them measure mid shoulder. The best is a bump gauge made with the chamber reamer. If your using the bump tool that comes with a Harrell's die, toss it. I personally like a little more bump, but if you like a zero clearance fit where the bolt falls half way thats fine. Bump as much as you like. Excessive bump will hide pressure because your taking thrust off the bolt face. You probably are seeing pressure.

Why do you like a stub made with the reamer but say to throw away the Harrell's tool? I have beat my head against the wall trying to diagnose problems with Hornady inserts and the Whidden things. I think I have good luck with the various Sinclair inserts but the Harrell's has always made the most sense to me when trying to diagnose a problem. Please, what am I missing?

 

[Gilbert Garza]

Basically the case is head spacing on the head and not the shoulder.

Can you please elaborate on “head” of case ?

 

[Alex Wheeler]

Why do you like a stub made with the reamer but say to throw away the Harrell's tool? I have beat my head against the wall trying to diagnose problems with Hornady inserts and the Whidden things. I think I have good luck with the various Sinclair inserts but the Harrell's has always made the most sense to me when trying to diagnose a problem. Please, what am I missing?

A gauge made with the same reamer as your chamber will have the same angle and radius' that your chamber does. The gauge that comes with the harrells causes problems. I have walked a lot of guys through issues and the Harrell's gauge has been the problem many times. If you are bumping more than .002 to get the bolt to close you should try a different comparator. The video is a work around for issues.

 

[Alex Wheeler]

Have not used them. All these universal tools can work or give problems. Its up to us to recognize issues when they come up. If you have to bump a case an excessive amount, stop and figure out what happening. If it is a comparator problem you can do like the video and just record the number you need to size to to make it work, or you can try a different tool. Sometimes its a diameter or even an extractor dragging.

 

[LCazador]

Can you please elaborate on “head” of case ?

The primer pocket, extractor groove, rim, and web are part of the case head. Measure diameter just ahead of extractor groove with .0001" micrometer. Hopefully your micrometer has a pointed anvil for proper measuring. Most sizing dies will not size this area.

 

[mikeeg02]

Have you tried to see if theres any pressure when you close the bolt with an empty shell in the chamber vs an empty chamber?

 

[Alex Wheeler]

Im not sure I follow you. A fired case is protruding .010" and a resized case .002" so your bumping .008"? Thats not right. Too much. First, knock out the primer on a fired case to be sure your not measuring off the primer.

 

[mikeeg02]

Hi Mike"
Yes
Empty chamber will close without excess pressure, a fired case definitely has pressure.

I mean any pressure. If you pull the trigger out of the action you shouldn't feel any resistance when you close the bolt. Once you've got the hang of it you can leave the trigger in place.

It can vary per piece of brass, depending on how much more or less spring back each piece has vs a different piece.

 

[mikeeg02]

If you have any "cock on close" it can give you false signs of resistance when you close the bolt to make sure its smooth with a piece of brass in the chamber.

 

[mikeeg02]

What aren't you understanding buddy ?

 

[Alex Wheeler]

If your getting heavy bolt lift from the very bottom of the lift, thats a pressure sign. Lots of things can make that pressure sign show up prematurely. It looks like you bumping plenty.