Thread: Sticky bolt?

Originally Posted by Tentman

This too - again easy to model on Quickload, if you care to measure a empty case, then one filled with water (level to case mouth, knock of any meniscus) I'll run it for you (barrel length required too) You could also compare the result with "other brass".

I'd agree that 46.0 gns of 2208 shouldn't be giving you problems, in "standard brass" its indicated at 61848 psi (just be aware CUP are not the same as psi) for 2724 fps at 18" of barrel.

OK just did a weigh up
Lapua mil brass (23 pieces)
173.8g average weight
0.6g SD
2.6g max variation

Federal brass (18 pieces)
176.3g average weight
1.06 SD
4.0g max variation

Lapua brass 52.2g WC

If you could please run this through Quikload that would be very interesting.
Cheers
James

Hmmm = the "standard" water capacity in Q/L for 308 brass is 56.0 grains water. It says that at 52.2 and with 46.0 of 2208 you are at 76,580 psi - but your mv would be more like 2840 from 18". You haven't mentioned your barrel length at which you get 2750 - this would allow a bit more "interpretation" of what could be going on . . .

Cheers

Originally Posted by Tentman

Hmmm = the "standard" water capacity in Q/L for 308 brass is 56.0 grains water. It says that at 52.2 and with 46.0 of 2208 you are at 76,580 psi - but your mv would be more like 2840 from 18". You haven't mentioned your barrel length at which you get 2750 - this would allow a bit more "interpretation" of what could be going on . . .

Cheers

18” barrel

Given it is 18" and producing 2750 then the max pressure is going to be a bit lower, indicated at 68-71,000 psi - Q/L is only a estimation tool - the results are not absolute, for example seating depth (COL) has a big effect on predicted results too

I run the same Lap brass in my 308 target rifle with good results, but I've never weighed it. I'll do so tomorrow and post the result.

Curious, does bolt thrust cause cratering of the primer like that ?

Weighted my Lap 308 brass (which I thought was Mil stuff). It holds 56.0 gns water. So maybe its not ex Mil at all. Just as well I worked up to 46.0 gns of 2208 with the 165's I'm running.

The difference in my load (according to Quickload) with 56.0 gns water brass is 60500 psi but if the brass was 52.2 gns water like yours the pressure could be 74,000 psi.

Oh - my Lap brass weights 178.0 gns empty so no correlation between brass weight and case volume!!

Originally Posted by Dead is better

Curious, does bolt thrust cause cratering of the primer like that ?

There’s no craters it’s just the camera zoom

Did you get that brass off me?

Originally Posted by Tentman

Weighted my Lap 308 brass (which I thought was Mil stuff). It holds 56.0 gns water. So maybe its not ex Mil at all. Just as well I worked up to 46.0 gns of 2208 with the 165's I'm running.

The difference in my load (according to Quickload) with 56.0 gns water brass is 60500 psi but if the brass was 52.2 gns water like yours the pressure could be 74,000 psi.

Oh - my Lap brass weights 178.0 gns empty so no correlation between brass weight and case volume!!

The mil surp brass has the crimp indentations around the primer pocket. The good stuff Dennis, does not.

Greetings again,
I have done a fair bit of weighing .308 W cases over the years and together with data mostly from Handloader mag have found the following. Kiwijames my weighing of Lapua brass marked 7.62 x 51 and 308 Win is much the same as your results of around 173 grains. This is a little heavier than Remington and Winchester recent production but lighter than Federal which is about the same as LC 81. The Lapua brass also has a slightly larger head diameter so some of that extra weight is here. There is a strong correlation between weight and case capacity. Other than a larger diameter head or differences in the rim recess size can have an effect on these in new unfired brass. In fired brass all bets are of because the size of the chamber has an effect. Handloader data showed capacity of between 53.4 and 54 grains of water for Remington and Federal cases. Winchester cases held more but more recent production is heavier, close to Remington. Measuring case capacity with water is a little hit and miss as any air bubbles will give a false (low) reading. All in all I don't believe your bolt problems are due to case volume. Also I would be very surprised if any Lapua military cases are head stamped 308 Win. The presence of the stab crimps may be needed due to non toxic primers. It would be interesting to know what the original rounds were.
One thing that you may wish to check is if the projectiles are close to or touching the rifling. For hunting ammunition there should be at least .05 mm (.020 inches) of jump. Hunting projectiles vary slightly. If they are too close the odd one may touch giving a pressure spike.
Regards Grandpamac.

Originally Posted by Gibo

Did you get that brass off me?

That solves it! They've been in the microwave then haha

Originally Posted by Dead is better

That solves it! They've been in the microwave then haha

Hard extraction/stiff bolt lift without any conventional pressure signs is often caused by brass not being sized enough by your dies, usually at the base.

Often the first couple of firings on new brass show no signs of stiff extraction, then as the brass expands after multiple firings and isn’t sized back down sufficiently by the dies, the brass doesn’t spring back enough after firing and grips the chamber walls causing hard extraction.

I suspect this may be what you are experiencing.

A small base sizing die, new brass or re-reaming the chamber with a slightly larger spec reamer are all solutions.

Greetings Again Kiwijames,
Another thought. The fact that the brass chambers easily each time suggests that the dies are doing their job. I am starting to think you may have a tight spot or ring in your chamber. These do happen, even in the best rifles, and can be hard to detect. There is seldom a problem with factory rounds and the ring can't be seen looking into the chamber. You may see a slightly shiny ring on the outside of the problem brass. The problem usually shows up as hard extraction after the brass has been fired a few times. Each time the brass is fired the body work hardens a little and springs back a little less. Eventually the body does not spring back enough and you get a sticky or hard bolt lift. In your or other posts above a lack of primary extraction is with the Forbes action is mentioned. This would aggravate the problem. As far as a fix goes setting the barrel back a thread and re cutting the chamber would probably be needed but you may be able to manage the problem to an extent depending on where the ring or tight spot is. Using once fired brass for hunting should stop the problem happening in the field.
Regards Grandpamac.