Problem with 75 grn Hornady moly Amax

[loose noose]

I recently got a Upper Barrel Assembly from Model 1 Sales in bull barrel 1/7 twist, and placed it on my Bushmaster lower with a Timney trigger. It' a pretty neat set up. With 52 Grain bthp by Hornady It'll shoot 5 rounds into a ragged one hole group. The problem I'm having is with the 75 Grn Hornady Moly coated Amax bullets.I've used RL-15, IMR 3031, IMR4198 (is what it likes with the 52 grn. bthp), Accurate 2230.The best group it shoots is 3" directly above the POA. BTW all my shooting is done at a 100 Yards. I've been reloading for over 40 Years and I believe I know what I'm doing. I've used different powder weights, and once fired cases all full length re-sized, with an oal case length of 1.750", the final loaded cartridge is 2.555 which barely fit inside the mag pul magazines. Any advice you can provide will be appreciated. Incidently I'm new to this forum so any info would be greatly appreciated.

 

[NCsmitty]

What barrel length are you using? Have you checked the twist with a cleaning rod to verify the 1in7".
Is your COAL 2.555 or 2.255? Have you checked your velocity with a chronograph?

Did you clean your barrel thoroughly before trying the Moly coated bullets?



NCsmitty

 

[loose noose]

It is a 20" barrel and yes I checked the 1 in 7" twist. The OAL length in the Accurate Reloading manual suggested a 2.250 with a 70-75 grn. bullet, I noticed the 2.255 OAL fit in the magpul magazines and chambered well also. I've tried 2.250 oal but there was no difference in the accuracy. I heard on another thread that some guns just won't shoot the moly coated bullets. Oh btw I allways clean the barrel before going to a new load. I have a Chrony but I haven't checked the velocity with that load yet, good point!

 

[bfoosh006]

Hornady does make two different 75 grainers in .224 , one is the AMax, the other AR mag length bullet is the 75gr BTHP , this one is meant to be used in AR mags. The AMax version can be used in ARs , but need to be loaded longer oal ( because of the ogive ) , and can't effectively be used in an A

The 75gr AMax is very similiar to the Sierra 80gr.... single load bullets.

http://www.hornady.com/store/Match-bullets/

 

[bfoosh006]

http://www.google.com/search?q=Can+I+load+the+75gr+AMax+to+mag+length+for+the+AR&rls=com.microsoft:en-us&ie=UTF-8&oe=UTF-8&startIndex=&startPage=1

 

[DaveInFloweryBranchGA]

You're using the wrong bullet for your application, as bfoosh006 said. Give Hornady and a couple of the other bullet manufacturers a call on their tech support line, tell them what rifle you have and get a recommendation. I betcha those groups with shrink with the right bullet.

 

[CSestp]

Military uses 1in7 20 inch with 62 grain. Don't know if that helps, but its what I know.

Sent from my Desire HD using Tapatalk

 

[MtnCreek]

If you loaded a 75gr a-max to fit the mag, the bullet should be seated so deep that the ogive is below the top of the neck. This will limit the bearing surface between bullet and case neck and with a lubed (moly) bullet, there is an increased chance of bullet setback when the cartridge hits the feedramp. I would pull any that are loaded this way and seat them as single loaders.

 

[loose noose]

If you loaded a 75gr a-max to fit the mag, the bullet should be seated so deep that the ogive is below the top of the neck. This will limit the bearing surface between bullet and case neck and with a lubed (moly) bullet, there is an increased chance of bullet setback when the cartridge hits the feedramp. I would pull any that are loaded this way and seat them as single loaders.

The bullet is not backing into the case upon chambering as I've checked the oal after running the rounds thru the rifle. BTW the 75grn Hornady is a boat tail Amax. I checked with Hornady and they said all my loads were within limits, but they couldn't tell me why my rifle apparently doesn't like them. I've had excellent accuracy with the 62 grn hpbt bullets using Accuracy 2230 powder and Federal Bench Rest Primers. Think I may give up on the 75 Grn Amax bt.moly coated bullets. Thanks for all the information.

 

[MtnCreek]

I tried loading the 75gr a-max to mag length and the ogive was below the case neck. I don't recall the length but my typical .223rem length is around 2.24. There was a visible opening between the bullet and case neck; no neck tension for a portion of the neck. Does your have this gap?

As far as your rifle not liking the 75a-max, that could be anything I suppose. You changed bullets and added moly, correct? May want to clean the moly out of the barrel and tumble it off some of the bullets to see if that is hurting your accuracy.

They didn't perform well for me (loaded for single feed), but I got better than 3" groups. If you're looking for high bc, give the 77gr smk a try, if you haven't already.

 

[loose noose]

I'll be darned you're right I just checked my last loaded rounds there is a slight gap around the ogive, but they are holding at 2.255 not the 2.555 I stated earlier. Man it's hell getting old. Guess I'll have to, pull them out a bit shoot them thru my Howa one at a time. or get some of those AR's bfoosh006 suggested. Thanks again sounds like my problem is solved.