Pressure signs with shorter OAL??????

[JoshcBoucher]

I was trying some shorter {mag length} test loads today. My "accurate load", for my remmy 700 is 2.94, or 2 Ks off the lands. 44.7 Varget, federal brass and federal primers. I prepped all brass the same and only changed the OAL down to 2.8 for 25 out of 50 reloads. {OALS are "representative" of where my Ogive measurements left the bullets.] So I shoot 2- 5 shot groups with my accurate load, and 2-5 shot, with the shorter. I had too much coffee and shot 3/4 to 1 in, at 100. The shorter 2.8 in. loads shot 1 to 1 1/2. Larger was what I expected, even though I'm out of practice. BUT, the shorter loads "locked the bolt" 4 times out of ten shots, and flattened all the primers. The longer loads shot fine, with no pressure signs. This ones got my head spinning. Could that slight change in case volume be enough for the results I got? Any thoughts?

 

[Aimsmall55]

That's a hot load for federal and I'm assuming a 175 smk???

 

[mattj]

Shorter seating decreases case volume which increases pressure.

This goes over it a bit more...
http://www.bergerbullets.com/effect...coal-and-cartridge-base-to-ogive-cbto-part-1/

 

[Aimsmall55]

Basically , you compressed your load, which added alot of PSI at ignition which led to the sticky bolt. You'd be VERY surprised how much pressure builds the deeper you seat..... Especially on a compressed load.

 

[JoshcBoucher]

That's a hot load for federal and I'm assuming a 175 smk???

Sorry .It's a 168 BTHP. My thoughts were: farther off the lands= lower pressure, and did not think the reduced volume would be such an issue. With no pressure signs for 300[ app]. previous loads at the longer length, I thought I had more wiggle room. So much for tunnel vision, and assumptions. guess I'm pulling the rest apart.

 

[HodgdonExtreme]

If I understand you correctly, you seated bullets ~.140" deeper and got high pressure?

No surprise, that's a giant change in seating depth.

Assuming the same bullets, brass, powder, charge and primer...

Starting jammed into the lands, pressure will decrease as you seat bullets deeper into the case. To a point. Then pressure begins to rise.

 

[Expert684]

Not only are decreasing the volume in the case, but you may be increasing the engagement between the bearing surface on the bullet and case neck.

 

[Bender]

One needs to read a bit more before continuing. No offense but that should have been common knowledge. Take it as tough love. Stop reloading for a day or two and go read some more.

 

[JoshcBoucher]

One needs to read a bit more before continuing. No offense but that should have been common knowledge. Take it as tough love. Stop reloading for a day or two and go read some more.

No offense taken. Thanks for the feedback. Thanks for the link, Mattj. This was a case of "I've been loading for 25 yrs., and I know what I'm doing" and a last minute decision to go shoot. Actually, I've done the same thing, before, but with much lighter loads. This was the first time with a "hot load "i.e. over book load max. The lighter loads were obviously more forgiving, and left me with the ASSumption that it was ok to do. This old dog just learned something new. I was hoping that I did know everything, and this was the famous coriolis effect.:-] By the way, I am reading a very informative book by Tony Boyer. The book of Rifle accuracy. I highly recommend it.