This Pressure thing

[Greg Duerr]

When your shoulders move forward so that your cases are a little snug or tight I assume your pressures go way up ,which will give you the possibility of Blown pockets and Higher than normal velocity...................Is this correct?

So when your seating your bullets into the Lands for Fire Forming this will cause high pressure so you would need to back off on the Charge

So any time your cases are real snug in your chamber so that there is some resistance to closing your bolt ..............that would result in some High pressure issues?

 

[Barrelnut]

The bullet being jammed is what causes the increased pressure. The fact that the case it tight in the chamber has little to do with it. UNLESS the necks are too long and causing excessive crime on the bullet because the necks are jammed in the throat.

 

[FearNoWind]

When your rifle's bolt is hard to close there's a good chance you're dealing with incorrect headspacing. Some firearms headspace off the mouth of the case, some off the datum point on the shoulder, some from other points on the case.
Improper head spacing can generate dangerous pressures, slam fire incidents, and other nasty things. With the firing pin and its spring removed from the bolt, most rifle bolts should close on a properly sized case with very little or no resistance. With some rifles there is no resistance, with others there is a slight resistance while the extractor passes over the rim of the case.
Read this:
Armorer's Corner - Headspace
and this
Reading Pressure Signs - MassReloading
If you have technical questions about your specific rifle you'd benefit greatly from a visit to a qualified gunsmith who can advise you on how to safely handle your firearms and ammunition.

 

[MagnumManiac]

The point I was trying to make is that if you HAVEN'T adjusted your seating die so that the bullet is NO LONGER touching the lands, then you WILL get excessive pressures with lower loads.
My other point is that short throats also generate higher pressures sooner.

I'll give you a tip, I fire form ALL of my brass to my chamber WITHOUT bullets, whether it's an improved cartridge or not. I do not know what groups my 22-250AI, 257AI or 338-06AI get, they've never had a bullet fired in them during fire forming. I use Red Dot and a twist of toilet tissue and fireform. This way, I never have to worry if my bullets are in the lands or not.
BTW, if the chamber is cut correctly, there is NO REASON to seat the bullets into the rifling, the .005" negative headspace is doing the job of holding the case against the bolt face.
It is common that the fireforming load gives impressive groups that the then fireformed cases cannot match, it is due to a better pressure curve, the science of which is too lengthy to go into here.
Basically, as the pressure starts expanding the case the pressure curve is gentler and allows a more progressive bullet acceleration, which gives more consistent barrel time etc, etc.

Cheers.
lightbulb

 

[Gene]

First, jamming bullets slightly (.005-.010") does increase pressure some, but usually not excessively. When fireforming, the bullet should be jammed slightly to properly form the brass. Pressures will not go "way up" if the powder charge is about 10% below max.
When the bolt closure is hard on previously sized brass, the shoulders need to be bumped back a thou or so. WITH FIRING PIN REMOVED, IF THE BOLT FLOPS DOWN ON A RESIZED CARTRIDGE, YOU HAVE EXCESSIVE HEADSPACE, WHICH COULD BE DANGEROUS. Ideal bolt closure is when the empty brass case closes with very little resistance. This indicates the case shoulder and chamber shoulder are in contact. And does not increase pressure.

 

[Greg Duerr]

Last night I used a tool from Sinclair that after trimming your neck way back you can insert this plug in to the case run it into the chamber and it gives you your Max case length. All my fire formed cases are well under the max case length. Then I checked to see if the shoulders had moved forward.
The thing is tha when I first fire formed my standard cases to the Ackley usiing IMR 4064 and a 80gr bullet the charge was three grains less than Max and all the cases Had super high pressure and all the pockets were shot................The Smith cut the chamber so that you dont need to seat your bullet into the rifling, and was told that standard cases will be snug.
I Did notice that when checking to see if the shoulders have moved forward that the FF cases that did not show any High Pressure were 1.700 while the High Pressure loads measured 1.704 Those were tight in the chamber. I set my FL Die to knock back the shoulders to 1.700
I also purchased some Winchester Brass ...............the Smith said that he fire formes using 40.0gr of H4350 then FL sizes the brass knocking back the shoulders by .002

So after fireforming I measure my cases set my FL die to knock back the shoulders by .002 I should be in the ball park of duplicating the cases that the Smith used to proof the rife..........................Everything being the same.............................Of cource I will start really low and work up with the RL 22

Any advice would be appreciated

This has been a learning experiance that has help me understand that you never assume anything..in reloading..................

 

[Greg Duerr]

My bullets are seated .001-.002 off the lands

 

[MagnumManiac]

My bullets are seated .001-.002 off the lands

This is your problem.

Cheers.
lightbulb

 

[Greg Duerr]

So what do you recommend? This is what I was told to do by the Smith who built the Rifle......................001 off He sent me a Dummy round with the 105 Berger and that's the seating depth I use...............

If that's my problem then you must have the Solution \\\

Im all ears

 

[jsthntn247]

So what do you recommend? This is what I was told to do by the Smith who built the Rifle......................001 off He sent me a Dummy round with the 105 Berger and that's the seating depth I use...............

If that's my problem then you must have the Solution \\\

Im all ears

The answer is to do proper load work your self. Throats lenghten over time, some quicker than others, and you neeed to know how to adjust for it. Buy the Hornady Oal measuring tool and learn how to find your maximum overall length. Then do load work to find the right powder charge using the OCW method then vary your Coal starting .005 off the lands and working further away. Bullet ogives can vary up to .005 on some bullets, when you seat them .001 off, some are jammed and some arn't.

 

[Greg Duerr]

I realize that the bullet ogive can vary thats why I measure each one and adjust the Bullet seating depth accordingly. I use Redding S Micrometer seating dies. Pretty much ever one needs to be adjusted down as I set it up so that they are about .002-.003 Longer than the Seating depth and adust each one.

Ive started load work from 4gr's under the Max for the standard .243 and the 105 at 40gr.................Yet at 43.5 I hit HIGH pressure and thats the end of that case. The issue is at 40gr up to 43.0 the accuracy is about 1.25 Where the Fire Forming load of 40gr of RL 22 and the same seating depth gives groups that average .3 Its the Fire Formed Ackley cases that give me the the Problems.

Once Fire Formed I Full Lenght size and bump the soulders back by .002

The whole thing that is puzzling is that the Smith fire formed Winchester brass and loaded it with 49gr of RL 22 Sent me the Proof load showing 5 shots at 100 .440 He told me that he has not heard of RL 22 being that sensitive and suggested I try another Lot , which I did.............same issue. Tried RL 25 same issue High pressure at starting Standard .243 loads.

This weekend I will try H4831..................................

What I will do is seat the bullets off from the Dummy round by .005 and work back like you suggjested. Thats the last option I have .