View Full Version : Ar15 with shielen barrel loosing velocity

March 3, 2012, 09:10 PM
I have a smith and wesson ar 15 with a 20 inch shielen heavy barrel 1 8 twist 223. Im having problems with dropping velocity.. Ive been told maybe a bad barrel, another told me the barrel heats up in the cold (20-30) degrees, and the cycling changes?.. Ime very stumped, this is the third barrel for this gun. I could also be haveing gas problems, too slow of powder.. been using varget , benchmark. h335 im going to retry tommorow, the only groups that were horizontal so far..

60 grain sierras velocity with benchmark dropped 75 feet per second in three rounds, typical with varget also..

Complicating things also is the wind here in montana.. Ill get a very good group, and .3 gr over will go crazy with a slightly different weight case set..

I also use a spray cleaner that has cleaner and oil, and i have dirty slightly oily brass..

I dont seem to be having fouling problems, i clean with solvent and patches. not using bore bright all the time wont cause trouble like this will it?..

Obvousely im grabbing at straws, Ill get a half inch group, then next time out it wont come close with as close a load i can get to it....

any help appreciated.. any thing that could be the cause or is this normal for ar15 in cold weather..

thanks dave..

March 3, 2012, 10:39 PM
Why are you on the third barrel for this gun?


March 4, 2012, 12:51 AM
Are you wiping the chamber and bore dry with 2 clean patches after you clean and oil it?

Does velocity change for rounds 4-10?

It is common for rifles to shoot differently after being cleaned. This is why match shooters will fire 2-3 fouling shots before shooting a match.

March 4, 2012, 12:57 AM
How many variable do we have to work with?

Can we assume you have run a few fouling shots,and you are not changing powders during these tests?

I am asking,is the rifle given a chance to stabilize?

It is the same barrel/bore condition for all three shots.I am very skeptical that the rifled hole through the barrel is the issue.

I have experienced strange unstable chronograph readings when the sun is low.Have you verified with a second chronograph,or is your chronograph mounted in a stable fashion?Tell us about your chronograph conditions.

Gas block,gas tube,barrel nut,bolt carrier all potential areas to look.

Priming?High primers?Neck tension?

March 4, 2012, 07:08 PM
loading proceedure.
comming home from the range i dry the cases on the stove. Lots of snow here

then size
then tumble
clean out media
run a .80 drill bit thru flash hole
check for split cases
check oal, re trim if over .0005 over lenght throw away if under .0005 in lenght... keep cases to .0005 of 1.750 so crimps will be uniform.
if case is trimmed, I outside bevel and lightly inside bevel with long angle bevel tool
primer pocket clean
weigh cases and sepparate into groups of .003 grains or less
add power
seat with redding target seater adjust to .001, and coalate to 1.766 lenght, ( that is the lenght to the rifling DIAMETER of the bullet.. this is measured
with a sinclair tool..

Im not able to do much with neck tension becouse if i turn the necks i wouldnt get much of a hold on the bullets for semi auto feeding.. i want all the tension i can get.. I could turn down the expander if you think it would help.

today i tried my 4 best loads close to home at 66 yards, slightly breezy.. i went out to chrono them but chrono was not working may need a new one.

so i shot them at paper two strung down two did not, so maybe im jumping at conclusions, but on other days chrono shows about a 75fps drop between ist and third bullet, could just be poor poweder loads, neck tenson, etc, etc..

first group was 1/4 inch, 66 yds, all rounds hand loaded into chamber and let button close action, then push assist. action was cleaned and lubricated, barrel was not cleaned becouse i was going to go home load some more and clean barrel
number one and two were on top number 3 was 1/4 inch low. sierra 69 grn hpbt, 24.5 re 15

I willhave to start shooting 5 shot groups i can see by the last target and will have more information.. and the dropping velocity could be ulnlucky random odds.
several chronographed events tho showed about a 75 fps drop from the first to third round..
I wish the chrono worked today it would have cleared up some things..

, I got a new target barrel, by evolution to replace factory barrel that wasnt too bad,, the evolution had burrs in the chamber one came out one wouldnt, brownells traded me for a shielen that had a fitted bolt... I was out the install tho on the 2nd barrel...

the barrel seems to shoot well with the 69 grainers probably becouse of the 1 8 twist, but i dont understand the wide velocity variations, ... 25 fps variation at 1000 yards is 7 inches with my .243.. 75 fps would be 21 inches at 1000 yards with that gun.. i think i could shoot 500-600 yards with this gun, so im trying to find out whats causing the velocity variations .. i can see fouling at the front end of the gas tube, could this be opening up when the barrel heats up and streaches? Is 75 fps variation in loads common in the ar15?

I know very little about semi auto rifles, obviosly. thanks dave

March 4, 2012, 08:43 PM
I just happend by the semi auto reloading instructions in the sierra manuel... I have turned down the expander ball .002 so i dont have to crimp, and willnot change powders without cleaning the gun between groups.. thanks dave..

March 6, 2012, 12:31 AM

It will do it after several groups have been shot..

example, with 69 grain sierras hpbt the 456 rounds of the day shot a 9/16 inch group at 100 yards, with number 4 high and 5 and 6 9/16 inch below that.

I then set up the chrono and chronoed the next two rounds with a cool gun, number 7 and
8. .. they were at 2754 and 2688 fps respectivly...

This is most likely a simple semi auto gas gun situation, and i just need to run into someone who knows what it is and why its happening, and how i can fix it..

Hopefully its not a barrel problem, some guys at accurate loading.com said the barrel could need to be cryoed, but would need multiple 10 shot strings to show if that is the case.


James K
March 8, 2012, 12:09 AM
Chronos are pretty delicate equipment and don't take kindly to cold, snow and wind. I suggest having yours calibrated, then using it on milder days (I guess in Montana that means above 0 K). Ammo also is susceptible to weather and ambient temperature and the speed at which it changes temperature (as when you take it out of a warm car and put it on the bench) can make a difference.

Then you chamber a round and fire. That heats the chamber. You fire another, same thing. Now the chamber is warm, so you load another round, but don't get a good sight picture so you wait a bit, allowing the round to warm up.

Or the cold-warm-cold-warm cycle of the barrel is affecting velocity in some way.

Just too many variables that have nothing to do with your loading techniques or data or anything inherently wrong with the rifle.


March 15, 2012, 04:42 PM
For those like me that are searching for accuracy answers while beginning with semi auto rifles.

Read the preface in the the sierra book about reloading for semiautos.

use good preferably new brass to start.. and watch for brass problems that dont happen very often or soon with bolt guns.. Sierra recomends winchester brass and keep track of number or rounds fired.. Ive sorted mine in 2 grain lots.. seems to be sufficent.

Pmc bass seems to spit easily and a tiny unnoticed split in the neck will raise havoc with groups big time.

Turn down the expander with emmery paper, as in the sierra book tells .002 to .003 for neck tension.
Auto Slamming the shell in can move the bullet forward up to .004 of an inch in some circumstances.. Find a load that shoots well at both lengths.. or great at the seated length and acceptable at the extended length..

Watch for comparated length problems with box to box bullet lots, ive even notioced the difference in sierra.. The only bullets that remain close in my opinnion are berger but they dont seem to make a varmit bullet for .223 ar 15

.. That ive found anyway.. Sierra 69 match bullets will fit the mag and may have a good length seating for your rifling..

My present load is win brass, 24.5 gr re 15, rem 7 1/2 match primer, 69 grain match sierra bullet. always work up your loads.

these loads shoot as well as the wind permits with my shielen 1- 8, 20 inch barrel from brownells with matching bolt from the factory..

first three rounds the other day at 300 yards were a 1 3/4 inch .. Flag was horrizontal, but horizontal with each shot... lucky to have a consistent wind pattern at that time.. Not always doable in montana..

If your looking for ultimate accuracy, a comparater from sinclair and an adjustable bullet depth seater from redding will be a tremendous help, keeping your bullets seated to the correct distance from the rifling to the first .224 diameter circumference part of the bullet.. Overall lenght can vary rifling to bullet full diameter distance considerably in some bullets..

having consistent neck tension with good brass and a consistent bullet comparated length is key to accuracy with semiautos in my way of thinking..

crimping was not working for me, it may be nessesary in combat or self defence situations..

And watch out for these new cheap electronic scales, the one i bought is pretty bad, up to .8 grains off on one reality check .

thanks for all of your help...

March 16, 2012, 01:07 AM
I really appreciate your follow up!Thats how we all learn.It is good to find the answers and get results,isn't it? Congratulations.

April 1, 2012, 07:56 PM
Further notes on my ar 15 accuracy search, 20 inch shielen upgrade barrel 1-8 twist..

With an aproximate 20 degree increase in temperatures ive gone to a redo of my load with 69 gr speer match king..( Keeping my old 20-30 degree results for next winter of course) I may have to map every 20 degree variation thru out my montana weather cycle. I gone to varget which is a hodgdon extreem powder that somwhat resists temperature changes..Hopefully i can get a wider temp range and accuracy.

this reworking of the load helped get my groups back in order quite well.. I was having a problem with temp change AND worn out cases again.. 7 firiings left me with half of my necks split.. Im keeping track of firings and it may be 5-6 fireings before i have to throw out the cases. A split neck seems to raise holy heck with groups..(duh)

Ive rigged up a sloaped stock design simular to a modern wood stocked Usa rifle, and it allows me to slide the gun forward into the correct target position so my bag and shoulder pressure stays constant. the sniper flat bottom stock design did not suit me for groups and repetivive shots.. the bag would compress with each firing and need to be fluffed back up with each shot causing time and dissimular bag pressures..

A shooter friend who shot an ar in viet nam said that i should put no pressure on the pistol grip, that is torque or shoulder pressure from that point.. At this juncture i must agree. I form a circle with my first finger and thumb and tighten the circle to fire.. It seems, for me the way to shoot this rifle for the most accuracy.. Im using a bipod in the woods, sloaped stock as i said, and about 6-8 pound pressure on my shoulder with my left hand.. were not dealing with alot of recoil here.

As in earlier post follow sierras published reloading book recomendations for neck pressure and powders..

In the field the scope height causes cant problems. the terrain can totally fool me as to what is level.. the scope sits about 2 3/4 inches above the bore becouse of stock design and this is very detrimantal to first shot accuaracy when the rifle is not level.. So i bought a string level that was level, check by putting on a surface at the store and reverse direction on the level and the bubble will set in the same place if it is level. I put the level in front of the scope on the picitiny slots.. (the level is 8 sided so it sets there fine..)

The temperature change and split brass snuck up on me and i found my self blaming the usual culprets.. Barrel nut improper tension, gun joints loose ( i did buy an accuplug from brownells, and i cant tell if it helps or not, probably some) its nice the upper and lower are nolonger sloppy.... Barrel length (shortness is at blame when im having trouble, and any mechanical thing imaginable, when all the time it was my inempt loading abilities not watching temp changes and brass degredation.. (again (:<{

first shot problems plaged me quite a bit, so i dont do a complete degreasing after every shoot..

After three times out with about 20-30 rounds each fired i degrease with breake free, brush on moble one with a small paint brush on wear points,, I started using moble one on the colt .45 when extremm cold weather was a concern. Its the spliperiest thing ive ever found and used by alot of intence officers in extreem conditions.
I then use white lithium grease on the places the bluing is worn off, and the gass rings.
On the second and third time out i clean the barrel and put a little more moblil one on the gas rings and a slight amount on the wear points.. this has been giving me better first shot accuracy, except for after degreasing and complete cleaning.. Im still learning these points..

Im finding these guns are different than the modern bolt action, but not neccesarily Inaccurate.. They are different, requireing dilligence to accomidate them..

last time out i hit the gopher block at 100 yards first shot (quite windy day). a gopher block is a 1 1/2 by 1 1/2 by 4 inches.. piece of pine.
then had to sight in the new load for left and right at 200 yards and hit the gopher block at the third shot,
After sighing in better left and right, the gun hit the gopher block effortlessly at 300 yards.. at 400 yards the gun, level, load, would not cooperate in 10-20 mph wind at all...

Ive noticed that very few bullets that fit the clip and overall lenght requirement for accuracy, And are of sufficent quality.. vmax 55, speer, bullets have poor repetibility in bore diameter distance to the rifling.. Especially box to box.. One vmax box change had an aproximate .020 ogive lenth diffence.. the boxes were consitent, but if you just used the same setting on your seater and started loading you would not have very good luck with that.. sierra and berger seem to be quite adequate.. Ive not worked with nosler much, and will probably not unless the sierra 69 causes problems, which it doesnt seem to be probable.. I havent found a berger that will fit my overall lenght requirements to fit the clip, and they dont make a hunting version of the 22 bullet line that im aware of.. Im told the sierra matchking front end will comeapartwhich is what i want for shooing in the field.. ,. Dave