Pressure to low??? Sticky bolt and ejector marks

[Aimsmall55]

I had an interesting thing happen which I can't understand other it (71.5) was too low a charge. Pp 4000mr. 208 amax. Rp brass fully prepped fgm215m. . 700 ss5r mils pec. 26" bbl. at 72.4 it was grouping .475". (4 shots at 240 yards ) with absolutely no op at all. I shot the 71.8 loads to get fire formed brass and got sticky bolt and ejector swipes. Alliant lists 72.0 grains max for a 200 Speer. So why it was like that is beyond me.
Also found an excellent load with the 215. 72.5 r22. Running 2940. Same charge weight with the 208 and 2945.
The 208 with 72.4 power pro was shooting running 2950 to 2960. With a zero at 102 yards it had a 4.8" drop at 240 yards. And shot lights out.
4 shots at 240 yards

 

[SPAK]

Bullet weight is only part of th puzzle to pressure. Bullet bearing surface, actual diameter, and construction play a part as well. That being said, I have also seen excessive headspace mimick signs of pressure with ejector marks and sticky bolt lift. Brass sized too small can contribute to this.

brass that is no sized enough causing a insufficient headspace condition can also cause sticky bolt lift and ejector marks. Typically if you close the bolt down on a round and it has resistance you probably need to bump the shoulders back some more. You should be bumping the shoulders .001-.002". If you require more than a very slight resistance to close the bolt you probably need to size the brass a little more, but not to the point where it closes as if it were an empty chamber.

Also make sure your rounds aren't jammed in the lands if they were developed off the lands...in a given lot of 208 amax bullets I've seen up to .010" variation in bullet length and base to ogive length... Perhaps it was a bad lot, but it can happen... So if you're seating to just touch the lands some of your bullets may be intact jammed....

I've not seen this firsthand but supposedly loads with too low of a charge will have sooted case neckss due the brass not sealing from under pressure...

A really fouled barrel with heavy carbon build up in the throat can cause pressure signs as well... We're your over pressured rounds the last rounds you fired. How many shots since last cleaning??

 

[Aimsmall55]

Bullet weight is only part of th puzzle to pressure. Bullet bearing surface, actual diameter, and construction play a part as well. That being said, I have also seen excessive headspace mimick signs of pressure with ejector marks and sticky bolt lift. Brass sized too small can contribute to this.

brass that is no sized enough causing a insufficient headspace condition can also cause sticky bolt lift and ejector marks. Typically if you close the bolt down on a round and it has resistance you probably need to bump the shoulders back some more. You should be bumping the shoulders .001-.002". If you require more than a very slight resistance to close the bolt you probably need to size the brass a little more, but not to the point where it closes as if it were an empty chamber.

Also make sure your rounds aren't jammed in the lands if they were developed off the lands...in a given lot of 208 amax bullets I've seen up to .010" variation in bullet length and base to ogive length... Perhaps it was a bad lot, but it can happen... So if you're seating to just touch the lands some of your bullets may be intact jammed....

I've not seen this firsthand but supposedly loads with too low of a charge will have sooted case neckss due the brass not sealing from under pressure...

A really fouled barrel with heavy carbon build up in the throat can cause pressure signs as well... We're your over pressured rounds the last rounds you fired. How many shots since last cleaning??

I should first mention I was mistaken about the 71.8 charge. The rounds fired with op were once fired with the shoulder bumped 2/1000"s. my headspace is 2.770 in a fired round so they all were were 2.688 at the shoulder. I checked every single one. Ismh that they were all 2.616" (sammi is 2.610 to 2.620) and annealed. The bullet lot is a 1000 round lot that I've been shooting for years. The variances in the ogive have only been -.001 to .002. And Bullets are all 1.540". loaded rounds were 2.888 to ogive and 30/1000"s off lands. As for brass, the brass is Rp brass that I bought 15 (50) bags of ssme lot and thoughly prep before shooting. Coal of the 208 load is 3.615 roughly ( long throat). I also shoot the 215 bergers and they are 2.903 to ogive and 3.674 coal average. They are touching the lands but not once had an issue with op.
As to cleaning, I actually cleaned the rifle right before I shot using Boretech Eleminator and Frog lube. With a possum hollow bore guide and a Dewey rod made for .30's. after cleaning I got all of what I could out of the chamber and throat using frog lube and wiped it as clean as possible. Then ran a bore snake 2 times to get out any left overs.
Maybe I didn't bump enough because the new brass with a 1.6 grain higher charge shot like a dream. I do remember having just a slight bit of resistance closing the bolt but that's the way I always do it. Keeping it as snug and not over working the brass. I pulled the bullets and dumped the powder back in can. I'll go back and check it once more. If there is an issue I have a redding body die that will fix it real quick. Thanks for your feed back. AS

 

[SPAK]

Good info, how did he chambering of the loads with the higher charge feel in comparison to the 71.8 loads??

 

[Aimsmall55]

Good info, how did he chambering of the loads with the higher charge feel in comparison to the 71.8 loads??

A bit smoother. But this was virgin brass. Extraction was smooth as a babys bottom. No swipes, no flaatened primers. I did go back and check and some shoulders were .002" too much. Meaning 2.772". I chambered one and .... Yep, TOO MUCH tension. Reason being I have another .300 win mag and although I do my best to keep them sorted my wife will come out side and just start throwing brass into my containers with no idea of what she's doing. I've got 6 containers for each rifle. 3 for 1x 2x and 3x brass labeled. You think this is the culprit??

 

[SPAK]

Most likely. Reason being is the brass has no where to springback to. When we bump the shoulders back the case is now slightly smaller than the chamber. Upon firing the case expands to chamber dimensions and run springs back about .001" to its previous size prior to firing. This amount of springback will lessen over the course of repeated firings thus the reason we anneal our brass. If the brass is already too large for your chamber, then fired it will expand but it will only return to a state as small as the dimension prior to firing which was already too large too begin with.... I'm guessing that's your culprit...

 

[Aimsmall55]

Most likely. Reason being is the brass has no where to springback to. When we bump the shoulders back the case is now slightly smaller than the chamber. Upon firing the case expands to chamber dimensions and run springs back about .001" to its previous size prior to firing. This amount of springback will lessen over the course of repeated firings thus the reason we anneal our brass. If the brass is already too large for your chamber, then fired it will expand but it will only return to a state as small as the dimension prior to firing which was already too large too begin with.... I'm guessing that's your culprit...

Well thanks a lot. I really appreciate your input. Had me scratching my head...

 

[SPAK]

No worries, I'm betting if you load up 71.8gr in new brass you won't have any issues. Normally I do my initial pressure testing with new brass to mitigate problems like the one you just described... It only took a couple times when I first started reloading using twice fired brass with a new load trying to discern whether or not I had a brass issue or a true pressure sign...

Good learning experience.

 

[Temp9]

Also, keep Frog Lube out of your chamber! I posted a US Army Research Laboratory study here once where lube in the chamber was causing M249 failures. This is a direct result of the lube slicking up the chamber walls so the brass can't stick. The end result is a massive increase in rearward force, more than enough to cause ejector marks and sticky bolt lift with lower loads.

Edit: http://www.dtic.mil/ndia/2011ballistics/11826.pdf

 

[Aimsmall55]

Also, keep Frog Lube out of your chamber! I posted a US Army Research Laboratory study here once where lube in the chamber was causing M249 failures. This is a direct result of the lube slicking up the chamber walls so the brass can't stick. The end result is a massive increase in rearward force, more than enough to cause ejector marks and sticky bolt lift with lower loads.

Edit: http://www.dtic.mil/ndia/2011ballistics/11826.pdf

Damn!! Thanks. I'll keep it away from there for now on.