Effects of reciprocating mass on accuracy? AR specific

[Tim K]

Gonna test again today and see if it's real. I'll report back.

[Erni]

Could it be the chamber specs on new barel are off?

[20X11]

All Approx Number just to compare.
Rate of fire‎: ‎700?950 round/min cyclic (11.67 to 15 hz)
So it travels about 0.086s to 0.067s to a cycle dep on mass of bolt and velocity of ammo.



- 0.35" bolt carrier movement for bolt to unlock,
plus 1.750" case length
2.15" to eject a case;
to pick up a new round, 2.75"
for last round lock-back, 3.2".

5.56mm NATO M855
Vmuz=922 m/s (3,025 ft/s or 36,300 in/s)


l=14.5" barrel
v=(36,300 in/s)
14.5in / 36,300 in/s

approx 4.00x10^-4 sec for bullet to clear out the barrel
0.4 mili sec


0.086s to 0.067s to a cycle to pick up a new round, 2.75"
How about approx how long would it take 0.35"?

0.067s/2.75in = time bolt open/.35"

(0.067s/2.75in) (.35in)= time bolt open
8.53x10^-3s =
or 8.53mili second=

therefore bullet would leave the barrel even way before bolt rotates.
Oscil of metal from explosion is more significant than bolt travel time.

Wouldn't you only need to use the distance from the gas port to the end of the barrel in the calculation since the gas system isn't pressurized until the bullet passes that point? Not that it would alter the conclusion of your math, but if we are going to do math...let's be accurate.

[MrPrena]

Wouldn't you only need to use the distance from the gas port to the end of the barrel in the calculation since the gas system isn't pressurized until the bullet passes that point? Not that it would alter the conclusion of your math, but if we are going to do math...let's be accurate.

Youre right. It is Gas operated.

It will probably take even longer for the bolt to move.

[TFOGGER]

Also, the math assumes that there is effectively 0 time to accelerate the bullet from rest to muzzle exit velocity. Clearly, this is not the case. Regardless, the time to muzzle exit is probably less than time to unlock the bolt.

[MrPrena]

Again this is just simple approx high school physics applied just to show significations.

I do not have a lab or classical/mechanical physics lab to do this experimental physics to go 99.9% and it will probably cost too much for individual to fund this.
(Probably theoretical part of calculation would take entire day).

t=0 is when V0 where we assumed muzzle vel.
Primer hitting and chemical reaction time would be prior.
We were just calculating the mechanical movement.
We can calculate the time of acceleration by change in velocity respect to change of time. Or velocity times change in velocity respect to change in distance.

[TFOGGER]

I know, just giving you crap...

[MrPrena]

I know, just giving you crap...

From this thread, I realized how much the barrel and metal or polymer flex may contribute to an accuracy of a rifle.

[Tim K]

The re-test was inconclusive. I forgot my little fan, and the mirage from the gun was awful. If I had to draw a conclusion, I'd say the lighter set up did shoot a little better with two different ammo types. I believe I'll load up a significant quantity of what I think is a good load and test more thoroughly.

I got to thinking that maybe the bullets are moving in the necks from the extra thump of the heavier system. I'm going to pull the firing pin and chamber some rounds with the charging handle and see if the seating depth is changing.

[BPTactical]

Or a bad carpenter blames his tools...