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What learned over time building AR's
- Thread starter budlight
- Start date
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I just got online to RCBS. It appears that they don't sell my total do everything machine anymore. Now they sell the Brass boss and the seperate Trim pro 2. Probably because they cost so much even 15 years ago. When you start buying all the different caliber attachments for trimmers and the inside/outside neck trueing. It might have been $1000 total and I wore out .223 trimmer heads. I still have a couple of yesteryear hand cranks hand champhering tools under my bench.
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I consider multi sights, flashlights, and laser as bling! LOL
My question to you would be: Are you a Vietnam Vet with in country ribbons? How many of our troops died because of failed m-16's? I was fortunate that I was in a NEC that continued to use m-14's and other quality weapons clear through the 80's.
Why U.S. Special Forces Loved to Use Captured AK-47s in Vietnam
The AK-47's dependability and the ability to surprise enemies were both factors in why American soldiers sometimes used the Soviet assault rifle.
nationalinterest.org
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My original 3 gun competition with 20 inch diamond fluting QPQ match grade 9:1 twist non threaded barrel. The sling is great for steading standing shots. The 9 twist is just perfect for bulk 62 grain HPBT which had a fantastic over .320 BC on parr with 69 and 75 grain bullets. No problem 3200 fps loaded to 5.56 pressures. To bad covid or some state like Washington put an end to the bullet manufacturer because the hpbt 62 dissapeared from the market.
But anyway I got 3 gun out of my system and now it's another squirrel gun with a 8 -32 power 56 mm objective. Super fine target cross hairs so you are not covering up Mr. prarrie dog when you are attempting over 300 yard shots. Just a pleasure to shoot. I need to get back to Wyoming my friends were out blasting this week end.
The scope mount lever locking is a nice item. The centeral rail block is for the Caldwell brass catcher.
But anyway I got 3 gun out of my system and now it's another squirrel gun with a 8 -32 power 56 mm objective. Super fine target cross hairs so you are not covering up Mr. prarrie dog when you are attempting over 300 yard shots. Just a pleasure to shoot. I need to get back to Wyoming my friends were out blasting this week end.
The scope mount lever locking is a nice item. The centeral rail block is for the Caldwell brass catcher.
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Can you detail your 1st AR a bit more? I am curious if you ever did any analysis on the poor performance with the 55gr rounds? You say when you dumbed down the loads to bring the veolocities down "it could group". Did you intend to say "it could NOT group"? At what range did you do your testing?
Reason I ask is I have the same twist rate barrel in an inexpensive AR (16" length, not Palmetto but I looked at them). I'm looking for thoughts on what to pay attention to. I am not to the point of reloading, but am studying that subject and am wanting to get in to it down the road. Your comment about 55gr and under rounds going sideways really got my curiosity up.
cohunt
Well-Known Member
Don't bother with milspec triggers, dont bother with "composit/plastic" receivers, always use adjustable gas blocks, I've had good luck with flat facing the upper receiver barrel mount area, I've had bad luck with proprietary parts, I like muzzle brake shims over crush washers. Light parts cost more if they are advertised as "ultra-light" but if you search around you can find light weight parts for a bargain if they aren't being sold as "ultralight" parts. Ultralight builds are more finicky when adjusting gas. Different powers are sometimes ideal when reloading and trying to get gas pressures right. I like larger than milspec charge handles, binary triggers are fun. You can build a pistol that will fit in a backpack or saddlebag. Technically a pistol can be carried concealed with a permit- rifles may be different depending on your state permit, the atf can't make up their minds and like to "interpret" things different all the time. Lots of people fear black rifles, but camouflage guns seem to be perceived as "hunting" rifles . People are dumb.
I could go on with more things I've learned but the most important one is that extra parts eventually grow into complete rifles !!
I could go on with more things I've learned but the most important one is that extra parts eventually grow into complete rifles !!
Velocity increases with barrel length. going from 16 inches to 20 inches can be in excess of 300 fps. As velocity goes up with the same twist rate so does bullet RPM. Excessive rpm will make a bullet unstable to the point that it is flying through the air at odd angles. When sighting in my 20 inch it would splatter all over the paper with keyholing. The bullets would be flying sideways. My buddy with a 16 7:1 shooting my loaded 55 gr got typical holes. So I down loaded to under 2800 FPS the same speed as the 16 inch barrel and it punched round holes.
cohunt
Well-Known Member
Excessive rpm makes a bullet unstable?
I said that I DO NOT like or use adjustable gas blocks on any of my gas guns. You have to use adjustable gas blocks on piston guns because that is what the kit comes with.
Plastic lowers from what ive seen are really junk.
Mil spec triggers might be up around 7 pounds. They work, but I attemped to lighten them with aftermarket spring, drilling out the hammer to lighten them, polishing the break area. So much easier to just buy 2.5 to 3.5 pound drop in triggers.
I still have a couple of worked on mill specs. Like this hammer weighs about 1/2 an out of the box. So it resets easier and impacts the primer less.
Very interesting. Thank you.
I have heard, also, that 1:7, as you allude to in a different way, can "over-spin" bullets. One example is some soft point bullets actually disintegrating in the barrel from the centrifugal force encountered at the higher RPM. The evidence of it is lack of a hole in the target, rather a spray of fragments.
I am curious, also, as cohunt questions:
Thinking about the conundrum further, with the barrel length you mention going from a 16" to a 20" increasing the velocity at the muzzle, perhaps it isn't necessarily a function of the velocity or RPM, but rather the pressure behind the bullet that is accelerating it through the barrel that gets to a certain point where it throws off the stability when it exits the muzzle?
I am not sure if this analogy will properly illustrate but one way to think about it may be the affect of backing up a bumper-pull trailer where you have to keep the hitch under the center line of where you are trying to go - and that takes a lot of work side to side to get the hitch back under the center as "pushing" it is inherently unstable. The faster you try to back the rig up, and the shorter the trailer axle distance from the hitch, the more twitchy the response - eventually to the point you can't control it.
I don't know, but this intrigues me. I wouldn't say the above dynamics (going to factoring in the velocity to get the stability back in the round) is a function of the quality of the gun, it is the physics at play. The question in my mind is how do you identify those physics and tune to them to get the results you're after? I believe that can be done, within reason, with any firearm/round.
The original m-16 had a 14:1 twist rate and a 20 inch barrel. Who ever made the chrome lines 7 twist 20 inch that I bought probably should have stayed in school!
If I bought off the sheft slower 55 gr fmj it might have been fine. Because slower velocity made it not key hole the paper. Or if I shot slower heavy bullets it worked. I just will never buy another 7 twist
If I bought off the sheft slower 55 gr fmj it might have been fine. Because slower velocity made it not key hole the paper. Or if I shot slower heavy bullets it worked. I just will never buy another 7 twist
Both over un under rpm are bad. Look it up on the internet.
Friction heat does cause the internal lead of a copper jacketed bullet to become liquid in very high velocity rounds. It explains why varmint rounds can devistate small critters. rotating at rpm over 250,000 on impact the fragments can disperse at almost 90 degrees.
When I was kid and given a 26 inch 22-250 and I was hot loading I had 50 ish grain hp bullets come apart on the way to target. Because bullets of that era were not designed for high 3000 fps. I lived near seirra bullets and talked to them and they sold me bullet designed for the 22-250 and 220 swift. The 22-250 could have been a great round if they would have understood twist rates and the advent of heavier and heavier .224 bullets
I saw these near a road while out in my side by side near my house. I didn't count but maybe 80 -100 Lake city .223 brass. So I resized and decapped. I then put them in my steel media wet tumbler for a couple of hours because of the small number. They came out beautiful like always like brand new. Inside , flash hole, and outside.
common Lake City annealed brass once shot
After cleaning and drying in the sun. Like new again
Then it's time for the dillion primer pocket swager before hand primer time.
common Lake City annealed brass once shot
After cleaning and drying in the sun. Like new again
Then it's time for the dillion primer pocket swager before hand primer time.
Barrel twist rate is just a number like one rotation for every 7 inches of barrel. Let's then max pressure load 40 gr .224 and 80 grain pills out of a 20 inch barrel .223. The 40 grain comes out of a 20 inch barrel at approximatley 3700 fps and the 80 clear down at 2700 fps.
The same barrel and same twist rate. The faster 40 grain will have a much higher RPM spin rate than the slower 80 grain. You can actually find the calculated spin rate formulas online. That is why longer heavy per caliber bullets require faster twist rate barrels to achieve stability in flight. They are going slower.
Over rpm a bullet and it no longer has a stable flight. It has Yaw and Pitch angles that cause it to fly sideways through a 50 yard sight in target. I was splattering the target with pie plate sized patterns.
