Using Longshot With 180XTP's?

[sqlbullet]

Oh...and if it is flinch, a flat bottom stop and stiffer main spring will soften the felt recoil, making it easier to overcome.

[The_Shadow]

sqlbullet, I understood the swivel link and its use to pull the barrel downward out of slide engagement, I still have to believe the recoil spring's applied pressure pushing the slide forward, has to be overcome, even before the rearward travel of the slide, moves enough to start the link's action to pull the barrel out of the slide engagement.  A recoil spring can also be so strong, that the forces of the fired ammo, can not overcome that spring pressure and too little slide travel or even no slide movement or ejection can take place, leaving the spent case inside the chamber or not fully ejected.  Not trying to be argumentative just trying to show situational awareness.  Alot of the physics involved has to do with the mass of the slide itself as well as the dynamics of the parts in action.

When talking about dwell timing, it is in microseconds, the higher impulse ammo seems to change these dynamics, so the further down the barrel the bullet is the better...as the slide does start to move, so too the recoil is being applied.  It as that instant, that the shooter feels the recoil starting, but the duration is throughout the full rearward travel of the slide and as forward travel of the slide carries it back to battery.

I think of competition shooters who use usually faster burning powders, the pressure spikes more rapidly and also drops faster as the energy is dissipating, whereas when we use the slower powders to develop higher gas pressures for longer time periods (again microseconds) to give added push to our projectiles.

[sqlbullet]

Me either (argument wise).

Argument here is whether spring rate influences dwell time, defined as the time the bullet spends traveling down the barrel.

You say yes.  Spring rates influence dwell time. I say no, they don't.  This is a long standing debate that can be found on lots of forums.

The simple answer to the question is so obvious it is obscure.  The time the bullet is in the barrel before it leaves can be derived from it's muzzle velocity.

Does changing a recoil spring change muzzle velocity?  No.  Obviously not.  The bullet spends the same time in the barrel whether you have a ten lb recoil spring or a million pound recoil spring.  You might encounter some stoppages with that latter spring though

Changing the spring does impact the slide velocity though.  Heavier spring, lower velocity.  That million lb spring would keep your action shut for sure.  In fact, a 1500 lb spring would keep the slide/barrel still for these loads and probably any safe 10mm load (yep...did the math).

Here is the thing that surprised me (it shouldn't, but it did cause I wasn't thinking).  I fact, I kept looking for an error that wasn't there.

Slide/barrel movement during dwell is static for a given bullet weight.  That is right.  The distance the slide moves during the dwell time is the same regardless of velocity for a given bullet weight.

Yes, more muzzle velocity means more slide velocity.  But it also means proportionally less dwell time.  The slide moves the same distance, faster.  In fact, for a 180 grain bullet in a 5" barrel where the barrel/slide combo weighs 2lbs the distance moved is .064" regardless of velocity (no spring).

Might changing the spring impact accuracy.  Almost certainly.  In battery, the muzzle is locked against the bushing.  The bushing is also in contact with the slide and the recoil spring plug which is acted on by the recoil spring.  Changing the spring will therefore have an impact on the harmonics of the barrel, just like one of those harmonic tuners for a rifle barrel.

I think my second assessment is the most likely.  You are walking your load up out of a harmonic sweet spot.  Keep going up and you will walk back into one.

[Desolo]

The way ive seen it explained as far as 1911s go  is the small radius/flat firing pin stop just changes how the slide interacts with the hammer, and the recoil energy will always be the same, its just people feel it differently.

Anything else it does to slow the slide down is an added bonus in .45's but in a 10mm it helps keep the slide from rocketing back quite as violently after unlock. A long while ago I read about someone on The High Road forums ( May have been 1911Tuner) that had ran a 1911 WITHOUT a recoil spring at all ( had to line up the bushing and a flgr after every shot) just to prove that the pistol wouldnt destroy itself if the spring wasnt there. Its pretty interesting and wish I had a link!

[sqlbullet]

It was 1911tuner that ran a gun without a recoil spring.

And you are correct.  Recoil energy is determined by the weight and speed of the projectile leaving the gun.  The energy is exclusively controlled by those values.  Everything we do with springs and stops and geometry is to alter how that energy accelerates the slide.  Ideally, the slide would loose all momentum .0001" short of full travel, and the recoil spring constant would be just strong enough to strip a round from the magazine and return the slide/barrel to battery.

Generally speaking, about a 10-12 lb spring is all you need to run the action forward.  14-16 lb springs are used for fudge factor in 45 acp duty guns.

It was Ned Christiansen (sp) of Michiguns who did empirical testing of flat bottom firing pin stops.  His methodology was this:

He put a Wilson Shok-buff in a full size 1911 running 230 grain/830 fps ball ammo.  He fired groups of rounds, I don't remember the counts, inspecting the shok-buff.  Once the shok-buff failed, he stopped, noting the round count.

He then repeated the test with a Delta Elite.  Round count diminished significantly.

Finally, he installed a flat bottom firing pin stop in the Delta Elite, and repeated.  Round count was very similar to the 45 ACP gun.  The implication was that the force the shok-buff experienced had been reduced to "near" 45 ACP ball levels.

Makes me wish I owned a really high speed camera and a Ransom rest.  Should be pretty easy to just measure the slide velocity changes with and without the flat bottom stop, and from that calculate the difference.

[Desolo]

It would indeed be a fascinating project, would also be neat to compare commander goverment and longslide variations aswell.

[sqlbullet]

If someone has a longslide they can provide the weight of I will plug it into my spreadsheet and report the calculated difference.

[The_Shadow]

sqlbullet, I still have to think that the recoil spring does indeed have an influence and that it is a measurable difference.

When I measured the different spring rates of my Glocks it requires more pulling pressure, just to start the slide moving rearward against the different RSA's.

Example:
Glock 20SF spring test Wolff Gun Springs 22lb RSA installed
It takes 6lb 4oz to start the slide to move from the locked position [The 22-Slightly over a pound difference 1lb 1oz to start the slide to move from the locked position over the factory RSA]
Full retraction at 22lb 9oz at lock open

Glock 20SF spring test Wolff Gun Springs 24lb RSA installed
It takes 7lb 6oz to start the slide to move from the locked position [The 24-Slightly over a two pound difference 2lb 3oz to start the slide to move from the locked position over the factory RSA]
Full retraction at 24lb 1oz at lock open

Glock 20Sf Factory spring test
It takes 5lb 3oz to start the slide to move from the locked position
Full retraction at 18lb 0oz at lock open

Not sure if it will make any difference in the 1911's like it does in the Glocks.
Can your mathematical model take that kind of difference into its equation?

[sqlbullet]

I guess I wasn't clear.

Spring does make a difference.  I was wrong about that.

We were both assuming the slide had moved MORE with the more energetic load.  And were arguing about what could counter that.

But we were both wrong about the change in velocity making a difference in dwell distance.

Velocity of the fired round does NOT make a difference in the amount of slide travel when the bullet leaves the barrel.  A faster bullet leaves the barrel faster, and the slide therefore moves that distance faster.  But the barrel and slide in a given gun will always move the same amount when a 180 grain bullet leaves the barrel.

The slide doesn't move more with the faster load.  It moves faster, but is in the same place when the bullet leaves.

[Desolo]

If someone has a longslide they can provide the weight of I will plug it into my spreadsheet and report the calculated difference.

Would a home postal scale reading work? I may be able to get a reading tommorrow, as a friend has a postal scale.

[sqlbullet]

Yeah..Nearest oz or half oz would be ideal.

[Desolo]

With barrel? Im assuming the barrel would be part of the reciprocating mass...

[sqlbullet]

Yes, but ideally weigh them separately.  My spreadsheet has different line items for them, though they are never used independently in the formula.

[Desolo]

Plans changed so I wasnt able to meet up with my buddy with the scale yesterday  I should be able to get to him next week. How many variables does the program cover, should I just weigh the barrel, then the rest of the slide components together? ( bushing and the assembled slide less barrel)

[sqlbullet]

When I weighed my Para, I weighed the recoil spring plug and bushing with the slide.  Barrel is separate.

The spreadsheet calculates the velocity and displacement of the unsprung moving mass at the moment the bullet leaves the barrel.  I need to upgrade it to include information about the spring, but without spring constant values that will not be accurate.  Haven't had a chance to look at Wolff Springs site to see if he publishes spring constants.