View Full Version : Diagnosing Deflection marks
Almost put this in ammo and reloading but it's really a technical question, not a reloading question.
I'm wondering what factors could be involved with causing the deflection strike higher on the case towards the shoulder rather than mid case as is usual.
http://home.comcast.net/~tedfs3/Images/Eject_01.jpg
Reloads: 1x fired LC 11 brass, 64 gr Gold Dot pulls from RMR, TAC powder running the hotter 5.56 data from Ramshot,
CCI #41 primers. Loading and shooting temps were above 80º from a few weeks ago. Loads were worked up,
these are just starting to flatten the primers. Next hottest load was a bit too much for my liking, settled on these.
Rifle: BCM BFH 14.5" Mid Length Barrel, VLTOR Low Profile Gas Block GB-2S, Battle Comp 1.5, BCM Bolt Carrier Group Auto (with BCM Extractor Spring Upgrade Kit ),
Colt H2 buffer, Tubb Flat Wire Buffer Spring. All riding on a Mega Upper/Lower billet set and a DD LITE 12.
The deflector on the Mega upper receiver is at a different angle than my BCM BFH 14.5" Mid Length Upper receiver but the Mega deflector is also shorter.
Not sure if that's the only cause behind the different strike mark or not, so thought I'd ask if anyone has some ideas.
Mega deflector on Left, BCM deflector on Right
http://home.comcast.net/~tedfs3/Images/Angle.jpg
polymorpheous
09-28-12, 01:08
Gas port size, buffer weight, carrier weight, and ammo all play a role here.
There is no one answer here given the aftermarket spring and heavier buffer you are running, on top of your hand loads.
Added a pic of the different deflector styles.
Not sure what the gas port size is on the BCM BFH midlength barrels.
I'll have to take a different BCM upper (built by BCM) to the range as well, test them both and go from there.
Run some factory ammo first, then the reloads and see if that changes anything. Gotta start somewhere.
Texas_Mike
09-28-12, 01:50
"BCM Bolt Carrier Group Auto, Colt H2 buffer, Tubb Flat Wire Buffer Spring"
This is the cause of your issue. Too much weight and spring tension. Your rifle is more than likely properly gassed with a correct sized gas port. Spent cases are being ejected earlier than normal during the cycle due to the slowed rate of the carrier. Use a standard buffer.
polymorpheous
09-28-12, 03:01
Gas port size is 0.625".
Gas port size is 0.625".
Oh shit.
polymorpheous
09-28-12, 07:38
Oh shit.
I got the same upper.
;)
Gas port size is 0.625"
:blink:
That's only in .750" and up diameter barrels, right?
polymorpheous
09-28-12, 07:52
Let me pull my foot out of my mouth long enough to state...
Opps!
Just saw his is a 14.5"
GP size is .0625" for a 16" barrel.
My mistake.
Get rid of theTubbs spring and get a blue Springco spring, and use an H buffer. The port size of that midlength is around. 074-.076 off the top of my head.
Just an update, haven't had time to get an H buffer with everything being sold out right now, still stuck with an H2. I waited too long...
Here's the difference between the Tubbs and a Blue Springco
http://home.comcast.net/~tedfs3/Images/Springs.jpg
Texas_Mike
01-05-13, 02:47
Just an update, haven't had time to get an H buffer with everything being sold out right now, still stuck with an H2. I waited too long...
Here's the difference between the Tubbs and a Blue Springco
http://home.comcast.net/~tedfs3/Images/Springs.jpg
I sent you a PM.
Are you working up your reloads for velocity or accuracy?
Are you working up your reloads for velocity or accuracy?
Both.
Best possible accuracy with the best reasonable velocity at 5.56 pressures. Accuracy is higher in priority but I'm not out to shoot ragged holes.
Suwannee Tim
01-06-13, 19:58
What is your objective with respect to the location of the dent? Do you expect to be able to manipulate the location?
......Here's the difference between the Tubbs and a Blue Springco
http://home.comcast.net/~tedfs3/Images/Springs.jpg
Which one is which?
Tubbs on top.
Those are around 17" long when new.
What is your objective with respect to the location of the dent? Do you expect to be able to manipulate the location?
Which one is which?
Yes, if possible. Not sure if it's viable given the Mega upper deflector has different geometry than the BCM. Change parts, see what happens.
Both.
Best possible accuracy with the best reasonable velocity at 5.56 pressures. Accuracy is higher in priority but I'm not out to shoot ragged holes.
Huh...Well, accuracy makes up for loss of kinetic energy.
It will be interesting to see what your results are in trying to manipulate your ejection pattern.
What's the best source for Springco springs?
http://home.comcast.net/~tedfs3/Images/Springs.jpg
I'd throw both of those into TEMPE TOWN LAKE and get a real USGI spring. :mad:
Tedfs,
Did you state any known difference between the two groups of cases shown in the first pic?
Were they fired out of different uppers or with different charges?
Or were they just picked up from the same pile and you noticed two different patterns?
All cases shown with the high mark were shot from the Mega upper.
The others were shot with the BCM upper, which does not have the Tubbs spring but also has lower deflector geometry than the Mega.
All cases had the same charge and projectile.
Just trying to diagnose if it's the different geometry of the Mega deflector, too much spring and buffer or a combination of either.
Do you have two lowers or just the one with tubbs/H2 buffer?
If you did, You can try swapping them.
Both uppers have identical barrels, firing the same ammo.
Looking at cases to create/diagnose the problem may not be helpful.
The feel of the rifle cycling should tell you something.
Look for how far cases fly and in what direction.
Check for lockback on the last round using a weak grip and weak ammo.
Then correlate the cases with all that other data.
The clearly different mega deflector is most likely the single largest factor.
If both uppers otherwise operate fine, I would not worry about case marks.
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