Does anyone know if there is a preferred cartridge length range, within specification, that provides for optimal feeds.
Thanks
I would say it depends on bullet weight and nose profile. Mag length limits rounds to 2.260". M193 rounds are a bit shorter and their nose profile is much friendlier than a heavy OTM.
I know my BM (no M4 feed ramps) does well with 55 grain ball, but with 68 OTM it’s hit or miss. I suspect if it had M4 ramps it would be more reliable.
I’ve done well with 60 grain V-max reloads, those feed OK and I beleive those are loaded to 2.250 - 2.255" range, but OTMs are a challenge. i will check on my OALs on the V-max loads when I get home.
Like Jmart said, mag length is about 2.260".
From my reloading bench time, it really comes down to the bullet profile as to how they feed. Mechanically I would think a rounded profile bullet would feed better than more straight taper bullet profile.
Jmart,
I think I have an idea where you might be running into problems. Your dies seat off a point on the ogive of a certain diameter. With some match bullets their length past this point varies a little bit, which is why some folk have meplate trimmers for bullets to get their lengths more consistent for mag fed guns. One of my match guns did really well with Hornady 75 grains seated long. The problem was that the Hornady’s varied in length a bit, once I started trimming I could seat them were they liked and I wasn’t getting them hung up in the mag or in feeding anymore. But that was from a hacked 20 round mag so I could seat the rounds out a little farther.
I have noticed the Hornady 75 BTHP’s do in fact vary as well. I was getting between 2.245-2.255(extreme). Had it set at 2.250, mostly within .002 of 2.250. But they all work 100% and can’t tell the difference in the RRA NM.
Mark
I’ve never really heard of many feeding problems with OTMs in 20" NM uppers, but I suppose those cycle a bit easier than carbine gas uppers. I can try seating a tad deeper to see if I obtain any improvement but I’m not going to invest in a meplat trimmer. I’ll send my upper off to Randall first and have him machine in some feedramps. (To be honest, after a couple of range outings I’ve come to the realization I’m not a good enough shot to exploit the benefits of heavy weight OTMs, so now I’m concentrating on more range time and shooting 55 grain ball to just get my skills up to a certain standard. Once I get there, then I’ll begin dabbling in better bullets.)
As I understand it, the prime reason to get a meplat trimmer is to get each bullet as consistent as possible to minimize BC differences. Not so much an issue at the 200 or 300 yard lines, but the deltas kick in at the 600 yard line, and even though in the course of trimming meplats you lower the BC a tad, you do get more consistent BCs across all the bullets.
I actually haven’t started reloading .223 yet but I measured the lengths of two different factory cartridges that I currently have on hand:
American Eagle 62 gr. FMJ - 2.210
Hornady TAP 60 gr.- 2.240
Haven’t shot either yet.
I previously had a jam at the feed ramp with AE 63 gr. SP and were the first fired from my BM Patrolman which has only 120 thru it. Just curious if length had any affect on functioning and looking for data before I used either.
Thanks
It’s not uncommon to have FTF failures with SP ammo in some AR’s. Extended feedramps might help, but you’re better off just avoiding the SP’s unless you need them for hunting.