question on COAL

[mdram]

i was watching this
https://www.youtube.com/watch?v=oRXlCG9YZbQ

he mention starting at max lenght and reducing it to tighten groups after finding your charge

question is, how much can the grendel be reduced and still be safe?

[Klem]

md,

Reducing OAL means reducing the case capacity, which in turn increases pressure. Not by much, but enough if you are loading on the edge of safe working pressures.

SAAMI limits are a conservative line in the sand. In a bolt gun you can play around with OAL and not worry too much. In an AR however it is a more fragile receiver and when you exceed SAAMI you stress the rifle. It will still be safe but something eventually breaks, from all reports on this forum it will be bolt lugs. AR's are the canary in the coal mine for overpressure.

Quickload it great for seeing the relationship between OAL and pressure. You can reduce the OAL and see how the pressure climbs and then reduce powder to match.

In an AR we are limited by the mag length for most bullets so starting 'long' means 58mm or whatever max your mag will take. That usually represents a big jump to lands compared to bolt guns so I don't think you are going to see much change (if any) group size by making it even shorter. By reducing case capacity and then reducing powder to match you also rob the cartridge of velocity which in a Grendel is already pretty slow.

In an AR I would start at the mag length and maybe do one length shorter; not slight - make it a fair bit shorter, and if no measurable improvement on the target give up tinkering with OAL, leaving that for precision bolt guns. If you do see a difference then sure, play around with increments of OAL. In an AR there may be a difference but you may never see it because the gun is not precise enough a platform. Every time we pull the trigger we struggle to match the same precision as a bolt gun.

In a bolt gun it is different. Start at the lands and work back in increments, but only after you have found the best bullet and powder. Powder and bullets make far bigger differences in group size and these are obvious. it makes sense to square these away first and then tinker with OAL, in the hope it will make it even better.

If you want to give us the details we can run a QL for you and give you some idea of predicted pressure.

[biodsl]

Klem...I appreciate your contribution to this forum. Thanks.

[Lemonaid]

mdram, when reducing over all length or increasing the seating depth the thing to look for is the point where the powder starts to be compressed by the bullet. A useful way to find that is to take a fired, unsized case and put in the amount of powder you want to check, insert the bullet you want to check (it should slide easy in the case neck) and measure the oal with light pressure on the dial calipers. That is the point of compression and for me is the limit for that combination of bullet and powder in terms of seating depth. On the other side is how great the oal can be with limits of magazine length and also how far out it can be seated until it hits the lands. Sometimes the load can have a very narrow window where it all four conditions exist. (no compression, fits in the mag, doesn't touch the lands and is within published safe load data for powder amount)

[mdram]

thanks all

[Cereal Thriller]

The less jump from cartridge to barrel with a longer COAL the tighter my groups got when doing my load development and ladder testing. Pushing the bullet harder and harder also aided in this for the grendel.

Did some final velocity tests last week and believe I have finally found the Willy Wonka Golden Ticket that I have been searching for. Just loaded up over 100 match rounds @ 2.276" COAL yesterday and plan really see what they can do very soon.



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[ported45]

i was watching this
https://www.youtube.com/watch?v=oRXlCG9YZbQ

he mention starting at max lenght and reducing it to tighten groups after finding your charge

question is, how much can the grendel be reduced and still be safe?

I had never seen that video until about 2 weeks ago, but that is how I ended up with my tuned loads for my Creedmoor. I started at max mag length (because I am a hunter and don't feed my bolt action one cartridge at a time) and reduced by 5 thousandths at a time. Just so happened that on two different bullets (143 eldx and 127 lrx) that my second seating adjustment yielded the best group size reduction and I was not intruding on my powder column. In the vid, he recommends adjusting seating depth by 3 thousandths at a time.

With my Grendel, I started with max mag length in my mags and worked up my load ladder and found a flat spot at 2395-2400 fps that puts them in the same hole. I'm not going to bother with changing my seating depth on this one. I just need to load up 10 of each of the charge weights and find out which one gives me my best numbers and stays in one hole.

[Trashy]

I like Eric, but he is chasing the lands like everyone else he just calls it “jam”, he measures the bullet in the lands and then backs off .020 Like everybody else.