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What causes variations in tolerance for pressure
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Picture of Mike_Dettorre
posted
...I am not talking about what happens when an action gives way...

I am talking about why will one load cause a sticky bolt in one rifle yet another rifle can go 1.5 grains higher

Is the major contributing factor chamber size?

Are there a couple of key variables or is it 7 or 8 potential things

Looking to understand say the top three things...


Mike

Legistine actu quod scripsi?

Never under estimate the internet community's ability to reply to your post with their personal rant about their tangentially related, single occurrence issue.




What I have learned on AR, since 2001:
1. The proper answer to: Where is the best place in town to get a steak dinner? is…You should go to Mel's Diner and get the fried chicken.
2. Big game animals can tell the difference between .015 of an inch in diameter, 15 grains of bullet weight, and 150 fps.
3. There is a difference in the performance of two identical projectiles launched at the same velocity if they came from different cartridges.
4. While a double rifle is the perfect DGR, every 375HH bolt gun needs to be modified to carry at least 5 down.
5. While a floor plate and detachable box magazine both use a mechanical latch, only the floor plate latch is reliable. Disregard the fact that every modern military rifle uses a detachable box magazine.
6. The Remington 700 is unreliable regardless of the fact it is the basis of the USMC M40 sniper rifle for 40+ years with no changes to the receiver or extractor and is the choice of more military and law enforcement sniper units than any other rifle.
7. PF actions are not suitable for a DGR and it is irrelevant that the M1, M14, M16, & AK47 which were designed for hunting men that can shoot back are all PF actions.
8. 95 deg F in Africa is different than 95 deg F in TX or CA and that is why you must worry about ammunition temperature in Africa (even though most safaris take place in winter) but not in TX or in CA.
9. The size of a ding in a gun's finish doesn't matter, what matters is whether it’s a safe ding or not.
10. 1 in a row is a trend, 2 in a row is statistically significant, and 3 in a row is an irrefutable fact.
11. Never buy a WSM or RCM cartridge for a safari rifle or your go to rifle in the USA because if they lose your ammo you can't find replacement ammo but don't worry 280 Rem, 338-06, 35 Whelen, and all Weatherby cartridges abound in Africa and back country stores.
12. A well hit animal can run 75 yds. in the open and suddenly drop with no initial blood trail, but the one I shot from 200 yds. away that ran 10 yds. and disappeared into a thicket and was not found was lost because the bullet penciled thru. I am 100% certain of this even though I have no physical evidence.
13. A 300 Win Mag is a 500 yard elk cartridge but a 308 Win is not a 300 yard elk cartridge even though the same bullet is travelling at the same velocity at those respective distances.
 
Posts: 10182 | Location: Loving retirement in Boise, ID | Registered: 16 December 2003Reply With Quote
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With identically prepared rounds, the key players will likely be:

- Chamber dimensions, esp. the neck. If the neck dimensions are tight the case may not be able to expand enough to easily release the bullet and thus increase pressure.
- Dimensions of leade, freebore, throating etc. The further the bullet can travel w/o resistance lowers pressure.
- Bore dimensions, including twist. The tighter the bore and fast twist impede bullet travel and increase pressure.
 
Posts: 3893 | Location: SC,USA | Registered: 07 March 2002Reply With Quote
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Picture of Mike_Dettorre
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Bob,

Thanks...


Mike

Legistine actu quod scripsi?

Never under estimate the internet community's ability to reply to your post with their personal rant about their tangentially related, single occurrence issue.




What I have learned on AR, since 2001:
1. The proper answer to: Where is the best place in town to get a steak dinner? is…You should go to Mel's Diner and get the fried chicken.
2. Big game animals can tell the difference between .015 of an inch in diameter, 15 grains of bullet weight, and 150 fps.
3. There is a difference in the performance of two identical projectiles launched at the same velocity if they came from different cartridges.
4. While a double rifle is the perfect DGR, every 375HH bolt gun needs to be modified to carry at least 5 down.
5. While a floor plate and detachable box magazine both use a mechanical latch, only the floor plate latch is reliable. Disregard the fact that every modern military rifle uses a detachable box magazine.
6. The Remington 700 is unreliable regardless of the fact it is the basis of the USMC M40 sniper rifle for 40+ years with no changes to the receiver or extractor and is the choice of more military and law enforcement sniper units than any other rifle.
7. PF actions are not suitable for a DGR and it is irrelevant that the M1, M14, M16, & AK47 which were designed for hunting men that can shoot back are all PF actions.
8. 95 deg F in Africa is different than 95 deg F in TX or CA and that is why you must worry about ammunition temperature in Africa (even though most safaris take place in winter) but not in TX or in CA.
9. The size of a ding in a gun's finish doesn't matter, what matters is whether it’s a safe ding or not.
10. 1 in a row is a trend, 2 in a row is statistically significant, and 3 in a row is an irrefutable fact.
11. Never buy a WSM or RCM cartridge for a safari rifle or your go to rifle in the USA because if they lose your ammo you can't find replacement ammo but don't worry 280 Rem, 338-06, 35 Whelen, and all Weatherby cartridges abound in Africa and back country stores.
12. A well hit animal can run 75 yds. in the open and suddenly drop with no initial blood trail, but the one I shot from 200 yds. away that ran 10 yds. and disappeared into a thicket and was not found was lost because the bullet penciled thru. I am 100% certain of this even though I have no physical evidence.
13. A 300 Win Mag is a 500 yard elk cartridge but a 308 Win is not a 300 yard elk cartridge even though the same bullet is travelling at the same velocity at those respective distances.
 
Posts: 10182 | Location: Loving retirement in Boise, ID | Registered: 16 December 2003Reply With Quote
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I might add that bolt face and chamber finish can play a role. A rough metal finish in those areas can cause a stiffer bolt lift with heavy loads.
 
Posts: 3893 | Location: SC,USA | Registered: 07 March 2002Reply With Quote
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Also the bolt to receiver contact. If one lug is doing most/all of the work, the bolt head can be forced to a slight angle (with the space filled by the case). To open the bolt you have to slightly size the shoulders back with the bolt handle.

Also the throat of the chamber will have a large effect, one that's .0005-.0010 over bullet diameter will "show pressure" sooner than one that's .003-.004 over bullet diameter (the tighter throat will also yield higher velocities / gr of powder used)
 
Posts: 2124 | Location: Whittemore, MI, USA | Registered: 07 March 2002Reply With Quote
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Any locking lug setback means the brass may have to be compressed as the lugs rotate out of the "dips".
 
Posts: 353 | Location: Southern Black Hills SD | Registered: 20 October 2004Reply With Quote
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. . . . and if the brass is not of the same internal capacity it can cause a difference in pressure. But more significantly is brass hardness; a swelled head due to soft brass will cause sticky bolt lift.
 
Posts: 13286 | Location: Henly, TX, USA | Registered: 04 April 2001Reply With Quote
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Picture of Bent Fossdal
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A "top-3"list would impress me.


Bent Fossdal
Reiso
5685 Uggdal
Norway

 
Posts: 1707 | Location: Norway | Registered: 21 April 2005Reply With Quote
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The difference is mainly caused by the action.

1; asymetric locking
2: Rearlocking
3: uneven bearing of the lugs
4: Rough champer finish on the body of the case.

The nature of the stick, is explained by the senario.
1 the presure rises, putting thrust on the action, and stretcinng it causing the brass to stretch untill it fills the gap.
The more elasticity that is build into the lockingsystem, the more stretch of the brass.

When the presure drops, the lockingsystem will try to returne to normal. The same will the brass.
There will always be a little "spring back" of the brass. But when the "spring back" of the lockingsysten, is larger than the "spring back" of the brass, you will have a heavy boltlift.

If you have a werry poor brassquality, or a werry poor chambersurfact, you will generaly have a reasonable light bolt lift, for the first part, followed by a werry stiff extraction.

Our Blow up test shoved that you on strong and symetric actions could handle presures over 100.000psi without having any sighns of heavy boltlift.
On rearlocking action, with capability to handle presures above 120.000 psi, you got sticky boltlift from the 60.000- 75.000psi range
 
Posts: 571 | Registered: 16 June 2005Reply With Quote
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