too much freebore

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14 years 5 months ago #4644 by banjobob
too much freebore was created by banjobob
Been having problems with accuracy in my AR10T, I loaded up sierra 168 MKs to the absolute max length for my mags - 2.865". Used my old stoney point COL gauge and got a COL of 2.944 to the lands. This yields a minimum freebore of 0.079". This sounds like a lot to me, is it???

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14 years 5 months ago - 14 years 5 months ago #4648 by lotoofla
Replied by lotoofla on topic Re:too much freebore
While this seems excessive, in reality yours is quite short. I know this is'nt what you expected, but let me explain. Using RCBS's 'Precision Mic' for 308win I've measued .090-95" from a Remington Model 700, ArmaLites AR-10 A2, and (T) using Sierras 175 Match King with an over all Length of 2.830" for comparison. By actually seating the bullet to an addtional .100+" this was confirmed when I started seating the further in. That's why custom (AR)gunsmiths are in great demand, and causing me to make my own uppers with 0.000" bullet jump to start with. This allows me to play with the correct bullet jump without exceeding max length. Your answere as to why, lies in the fact that manufactures are CYA because of the few reloaders that don't know when to stop even after blowing up a rifle or two. An example is the Ruger P89 in 9mm Luger. The fired cases come out of it with a case mouth diameter of .390" essentialy a cylinder the case originaly was a tapered case with a mouth of .376" before firing. The fired cases would'nt go in my RCBS carbide die without having to be hand fed each time. Bullet diameter is .355" but the Rugers groove dia. was .358". Bullet jump was .081" using Hornadys 'Air Force' bullet with and oal of 1.155" (max length that works through the magazine). So what happens is any HOT loads get defused because of the big chamber an long throat. While the ammo you have will fit in a SAAMI chamber, most manufactures 'fudge' the numbers so that only the headspace is correct.
Tom
Last edit: 14 years 5 months ago by lotoofla.

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14 years 5 months ago #4654 by a Guest
Replied by a Guest on topic Re:too much freebore
Banjobob your problem is in the barrel or the fit to the receiver or a combo of all. Get your barrel bore scoped. You have to have some minor bullet jump because engraving the bullets in the lands on the auto loaders reseats the bullets, causes damage in the throat area and reshapes the bullet at the contact point. I had one of my NCOs at AMU go through the entire process. Indicating the bullets before and after chambering with engraving contact and showed that they had moved up to .020 and concentrisity was knocked out to .008 to .012 range. If you run the zero bullet jump try taking a jackhammer to your throat area it will have the same effect. I had rather have the throat area as cut and the lead cut in good shape. This aint the same as closing a bolt slowly by hand. You need some bullet jump with all auto loaders but an estlablished STD has yet to be found. I have some ideas as to whats good but thats why I have a reamer ground to the bullet to be used. For some calabers I have 3 different reamers depending on what bullet is used. Your .080 freebore aint your problem. Theres an old saying you got a good barrel or you aint.MSH

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14 years 5 months ago #4659 by GONIF
Replied by GONIF on topic Re:too much freebore
Exactly,that's about right for a semi auto . Your problem is else where . I would call Armalite and see what they say .

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14 years 5 months ago #4662 by lotoofla
Replied by lotoofla on topic Re:too much freebore
Some thing to think about, the Remington M700 I wrote about earlier has a BJ of .095" and will shoot under 1.0" all day long at 200yds. It's a cheap rifle with a light weight barrel, plastic factory stock, and a Sheppard 3x9 scope. Factory trigger set at 3#s. If your itching for the load info here it is: G.I. cases, CCI STD primer, 95% load of H4895 for a Sierra 175gr Match King. COL 2.830". This was'nt a developed load, it's a starter load. In my AR-10 it's all over the map. Tom

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14 years 5 months ago - 14 years 5 months ago #4668 by GONIF
Replied by GONIF on topic Re:too much freebore
If you are the original owner of the rifle Armalite will make it shoot right if it is a rifle problem . Did you check to see if the scope and mount are tight ? Is the scope good ? I would buy a box of Fedral Gold medal match in 168 or 175 grain and see what happens . If you still can't group at 1.5 moa at 100 yards than you need to call and get a RA # and send it back to Armalite explaining that you can not get good groups with it and the Federal Gold metal match . Don't tell them your pet loads don't work in thier rifle . make sure your scope or loose mounts arn't to blame B4 you send it back . My AR10T will give me 1/2 inch groups with my 175 grain pet load and 3/4 of an inch with Federal Gold metal match 175 grain . You can count on Armalite service to fix it if it's the rifle .Just for fun try 46gr Varget, 155gr Scenar, Win brass, CCI BR2 primer, .003" neck tension, COAL 2.842"
if that won't give you a 1/2 inch one hole group in an AR10T ,you or the rifle Ain't on the job.
Last edit: 14 years 5 months ago by GONIF.

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