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Where is my pressure coming from?

 
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  #1  
Old 09-27-2012, 08:44 AM
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Where is my pressure coming from?

I am stumped... I have a 700 in 375 ultra, I worked up a load with 270 tsx and 98 gr. of H4350 (3150 fps) It ended up being a little too hot and was stretching primer pockets after about 2-3 reloads so I backed it down a half grain, then another and so on I am not down to 96.5 grains 3030fps and the more I shoot it at 96.5 grains the harder and harder ir has been to open the bolt. I was only neck sizing but decided to FL size once and it didnt really do anything different. Still has bolt click and a couple times I have had to beat the bolt back. It does fine with an empty chamber. I bore scoped the chamber/throat to make sure there was no carbon ring or anything that looks like it may be causeing an obstruction to increase pressure. There is some copper in the bore and there is a chance I have not been getting it all out. I use wipe out and gave it the boretech test and it passed. Next time i think its clean ill borescope it to be sure. I know I can just keep backing off the powder till pressure is ok. but with it getting worse and worse each time I fire 96.5 i think there is more to it. I am about 50 fps over book max with a 2" longer barrel. Also im on the 5th firing and my primer pockets are still nice and tight. I am hoping its a copper build up and I just need to be more thourough with my cleaning but...im a little skeptical...throw me some ideas guys.
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Old 09-27-2012, 08:50 AM
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Re: Where is my pressure coming from?

Make sure you are getting the shoulders back far enough.
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Old 09-27-2012, 08:52 AM
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Re: Where is my pressure coming from?

Check! that was one of my first thoughts. I have the Sinclair case gauge and it measures fine, and it chambers fine
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Mike

Anything less than overkill is underachievement!

" Real elk guns start with the number 3 or bigger and blow two holes, one in and one out." - My Dad
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Old 09-27-2012, 09:17 AM
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Re: Where is my pressure coming from?

Tight neck? Have you tried putting a bullet into a fired case? I ran into that problem with my 243, only found it when I tried making a dummy round for a new load. Or measure just ahead of the case head, could be you have excessive headspace and the cases are expanding beyond their ability to spring back.
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Keep in mind the animals we shoot for food and display are not bullet proof. Contrary to popular belief, they bleed and die just like they did a hundred years ago. Being competent with a given rifle is far more important than impressive ballistics and poor shootability. High velocity misses never put a steak in the freezer.

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Old 09-27-2012, 09:19 AM
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Re: Where is my pressure coming from?

Quote:
Originally Posted by Joe King View Post
Tight neck? Have you tried putting a bullet into a fired case? I ran into that problem with my 243, only found it when I tried making a dummy round for a new load. Or measure just ahead of the case head, could be you have excessive headspace and the cases are expanding beyond their ability to spring back.
I wouldnt think so in a factory chamber but ill check that! very good idea thanks joe....anyone else with ideas?
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Mike

Anything less than overkill is underachievement!

" Real elk guns start with the number 3 or bigger and blow two holes, one in and one out." - My Dad
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Old 09-27-2012, 09:32 AM
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Re: Where is my pressure coming from?

Here a a few dumb questions.

Any change in Powder lot? Primer lot? Bullet lot?


Is this the new brass you just got? How does it compare in weight & capacity to the first batch you used? Have they been properly trimmed?

Any funny looking marks on you case after extraction?

I just can't see fouling causing pressure problems. Sure would make it shoot like crap; but excess pressure?



A lot of redundant questions I know. Just rambling off the top of my head.


t
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Old 09-27-2012, 09:38 AM
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Re: Where is my pressure coming from?

Quote:
Originally Posted by Outlaw6.0 View Post
Here a a few dumb questions.

Any change in Powder lot? Primer lot? Bullet lot?


Is this the new brass you just got? How does it compare in weight & capacity to the first batch you used? Have they been properly trimmed?

Any funny looking marks on you case after extraction?

I just can't see fouling causing pressure problems. Sure would make it shoot like crap; but excess pressure?



A lot of redundant questions I know. Just rambling off the top of my head.


t
I have used the same brass as before and new brass, same bullet lott same primer lott different and same powder lott (just opened a new jug) cases are trimmed and deburred. extracted cases look fine (other than being stuck in the chamber pretty tight) I dont see fouling being the problem either but its the only thing I can think of that could possibly be getting worse as I go...
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Mike

Anything less than overkill is underachievement!

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