Old fart needs some advise

[Grandpa]

Just need some input from you fellas that have been loading the Grendel for some time. First I thought I had a good load worked up with 123 SST and 8208 but accuracy did not hold and pressures was an issue. So here's where I'm at with 123SST and 120 Sierra HPBT as soon as I get groups at 1" MOA 100 I show pressure sign. case head scraping / ejector pin / a couple had extractor marks etc. These are signs that tell me to back down so I did by as much as 2 grains of 8208XBR. When I do this my accuracy goes to 1 3/4" MOA and bigger.
After trying to explain that here's what the 107 gr HPBTs do with Benchmark low end load 27grs 3/4" MOA no pressure signs 27.5 grs same but not as accurate, 28 grs groups open up and slight pressure signs , 28.5 grs accuracy is so so but signs of pressure. This I understand and can work with it 5/8"s groups I can live with as it has potential.
The 123 and 120 gr are the ones that puzzle me. I have tried CFE 223 and Benchmark on the heavier bullets with the same results.
The barrel have is a BCA 18" fluted 1/8.
As I stated before I have moved from a 16" no name barrel to this 18" BCA. If this were a 223 or 308 and was doing this I would have sold the whole outfit by now but this little bugger is like an addiction. In fact I found a Ruger American in Grendel in a local GS and am thinking about getting it.
If any of you long time users have any thoughts on this I'd appreciate your feed back.

[NugginFutz]

You never mention what charge you’re using for the 123 SST and the 120 Sierra. My personal experience has been that, with 8208, anything near or over 28.5 grains has been where one must watch for issues. My 22” BHW likes the 123 ELD / Amax over 28.3 gr. The 120 SMK also shot very well for me at 28.3 grains. I started my load work up at around 25.5 grains, used .3 grain increments, and found one or two other promising nodes along the way.

As far as CFE223 is concerned, many of us have had good luck but others, such as myself, have not. I can’t say why that may be.

If you haven’t already, I highly recommend you get the handbooks found on the AR15 build box industry partners forum. They will provide you with a plethora of successful and, in most cases, pressure tested loads. (Vol 2, I believe).

Lastly, I’ve been reading where some of the guys buying the BCA barrels have been having “hit or miss” luck with them. Those who couldn’t get them to shoot and returned them have generally been satisfied with the attention they got from BCA (replacements/refunds/etc.).

Good luck.

[Grandpa]

The 8208 powder charge is 27 gr which is fairly accurate but is building pressure

[VASCAR2]

[grayfox]

Use of a chrony and doing some ladders is very important to developing good loads for the Grr, at 52 ksi pressure signs in brass develop too late to be good indicators, large delta-MV changes show up w/ the crony (not to mention that a sharp edge on the ejector pin can cause scrapes that aren't necessarily over-pressure). Also when working up loads I'd use a smaller delta than 0.5 grs (doing it for the first ladder is ok, 1 shot per load...) -- I try for something just less than 1% (ie, 0.2 or 0.3 grs), a rule of thumb that can help is that accuracy nodes tend to be about 3% load between nodes, so 0.5 jumps can easily miss them.

Another powder worth considering for the 120 class is AR Comp, not as temp sensitive as CFE (altho cfe is still a good one) -- max IIRC is 28.0 for the AR chamber. As always start low work up.

BCA has definitely had its troubles with short chambers, but it's already in hand so hopefully it will work out for you. Using go/nogo gauges and a head space comparator might be in your future so you know what you're dealing with.

[kev500]

I have seen on many different forum's that AR comp is also very good, in fact it may be best with SBR , I saw someone who said he gets 2280 fps with a 12.5 barrel with a ABLR 129 ? not sure but if anyone here has knowledge on SBR's and best powders for them please let me know thank you. I am in the process of getting my form 1 done, paid tax stamp, now must get kayos code and finest it, but 10 months wait , oh my

[grayfox]

Welcome to the horde Kev...
OP is asking about advice for his 18" barrel, maybe you'd want to start a thread on your 12.5 questions, you'll get more focused answers that pertain to it that way.... either here in the reloading section or in the AR's section... good choices.

[Lone Hunter]

The 8208 powder charge is 27 gr which is fairly accurate but is building pressure

How deep are you seating your bullets? I've seen where several people had short throats on BCA barrels and used a reamer to open them up.
I run 27.3 GRS of 8208 with very good results out of a BHW 20" barrel with 123 ELD M. My 1500 Howa Mini Action runs higher charges but it's a bolt gun. The load I'm using shows no pressure problems and I just don't see trying to hot rod stuff anymore. In my younger days the faster it went the better I liked it. I use CCI 450 primers. Try some 123 ELD M. I got the SST to shoot ok but not to my liking. If I were you I would either send the barrel back to BCA or sell it and put that money towards a good quality barrel. JMHO..

[Grandpa]

My seating depth is 2.260 and all bullets are checked in chamber with dummy round for lands marks. I'm getting 5/8 to 3/4" groups at 100 yds with 27 gr of Benchmark and 107 gr Sierra HPBT which is a very light load as soon as I go up in powder charge accuracy is lost. With TAC 26 gr and 120 Sierra HPBT I'm a little under 1" MOA / 100 yd there again .3 gr increase of powder accuracy goes to 2".
I'd like to know if anyone else is having this experience.

[grayfox]

Hard to say definitively if you're on a node at 27.0 without a chrono but let's assume you are. In raising the charge 0.3 gr you shouldn't normally expect to still be accurate, as that takes you "off node" so shots will open up; this is a normal consequence of what's called barrel timing, where the pressure-wave propagating (a "donut" shaped longitudinal wave) in the steel barrel is at or near the muzzle tip -- this leads to inconsistent forces on the bullet right as it exits the muzzle, and thus each bullet fired tends to go off in somewhat wild directions. Dan Newberry, and then Chris Long wrote about this in their papers. (the long family.com).

Personally I wouldn't expect to see another node until somewhere around 3% different, or maybe about 27.8-28.0 for Benchmark. Granted you might not be able to get that high in your barrel. Again the suggestion that your barrel might be one of the BCA "problems-children" but hopefully not.

Maybe try a different powder to see how it works? I'd suggest H335 or possibly TAC, they seem to have a decent weight range for the 107. H335 is listed in Hodgdon's mag for load data, TAC is in the Sierra load data pdf online.

[grayfox]

Excerpt from a paper I wrote adapting their work:

http://www.the-long-family.com/OBT_paper.htm