Grouping Differences Between Guns?

[Magsz]

Heya guys,

Humor me, ive got alot of questions.

Im a new reloader, ive always shot factory ammo and ive shot ALOT of it.  Ive never really spent any time on the bench but after developing my own loads, for peace of mind, i started benching my gun.

I have two CZ's.

A CZ 75 Shadow Target and a CZ SP01.  Both triggers are identical in their setup and both guns have the same front sight, a dawson .100 thickness front.  They are also the same height.

The SP01 is using the CZ Custom "tactical" rear sight.  This gun shoots one inch high of POA at 25 yards.

The CZ shadow has the adjustable Kensight rear.

The SP01 is a tack driver with the following load:

Montana Gold 124 grain JHP, 4.1 grains N320 loaded to 1.087 length.  I have checked the crimp and there are no marks on the bullets.  Post crimp the rounds are measuring .377.

At 25 yards i am able to pull 1.5 inch groups out of the SP01.  With the shadow...i cant group....at all.  When the gun DOES group, it is WAY left of the POA, im talking like  six inches left...

The Shadow has 5400 rounds on it at this point.  The SP01 was bought used but IVE put about 500 rounds through it so the total round count is unknown.

So...what gives guys?  I have no clue why my shadow wont group, nor will it even hit my POA.

PS, just to rule out variation, all headstamps were winchester.

The circled area is a five shot group out of the SP01.  The errant shots to the left are all from the Shadow.

[FireMoose]

"Post crimp bullets measure .377" this doesn't sound right. Jacketed bullets for the 9mm should be .355-.356.

[1SOW]

He's measuring the taper crimp at the mouth.

[noylj]

1) barrel differences
2) chamber differences
3) barrel lock-up differences
4) Sight picture differences
5) No two guns are same differences
If the gun with adjustable sights shoots a decent group, then adjust the sights to POI.

[1SOW]

Nice group with the SPO1!.   How did the Shadow Custom Shop target group look?Just some guessing/possibilities even though it shows you can shoot:

The SPO1 is well broken in and the 75 Shadow isn't.  Is the notch on the SPO1 rear the same width as the Shadow. ?  Have you weighed the trigger pulls?  It "looks" like the trigger finger was pushing the Shadow to the left.  The grip and the trigger press.

Also,  I really would retest using a less cluttered target with NO Distracters and a small highly visible POA,  and BREATH '. 
Internet guessing kinda sucks, but it likely is in here somewhere.
.

[Magsz]

The gun with the adjustable's is not grouping.  The left side of that target is all the cz Shadow Target...Yech.

Also, to correct the POI issue i would have to crank the rear sight blade basically OFF of the gun all the way to the right...lol.  That CANNOT be right.

Even at 15 yards i was getting weird fliers to the left with the Shadow Target.  The SPO1 was dead center with what i regard to be a "normal" deviation.

[Magsz]

I wanted to address this separately.

I keep a range log for the pistols.

CZ Shadow-5467 rounds
CZ SP01-600 from ME (i have no clue what the prior owner did with it but it certainly didnt look well worn when i bought it)

I would say that almost 6k rounds through the shadow SHOULD have it adequately broken in.

As far as the groups with the shadow goes...everything on the left side of the target is from the shadow...its all over the place and there ARE no groups lol.  Just a cluster of crap on the left side of the target.

The triggers on both guns are EXACTLY the same even down to the pull weights.  Even with the firing pin block the SP01 comes in at 2.4 pounds as does the shadow in single action.  The only real difference mechanically is that the SP01 has a longer reset due to the aforementioned firing pin block.  I used the same magazine, the same rest height, the same hold and the same trigger press between guns.

The rear sight notch on the Shadow Target is .120

The rear sight notch on the CZ custom Tactical is .135.

I would think that the tighter rear notch on the Shadow Target would actually be a BENEFIT to shooting tight groups...

This really does have me confused.  I had another shooter fire both guns this evening and his results were the same.

The very first day that i got the SP01 i shot a group very similar to the above and i chalked it up to the gun simply being a laser gun.  Still, the fact that my shadow doesnt GROUP bothers me.  I dont mind if its a three or four inch gun at 25 yards, i just want the darned thing to pattern and it wont.  Hell, i had a few random fliers on the RIGHT side of the target out of the Shadow....

Could a .355 projectile be too small for the shadow and JUST right for the SP01?

[1SOW]

Oops, I got it backwards.

I use the same bullets at 129 PF in three different CZs.  They all chrono pretty close to the same.  My son's SPO1 Shadow is the third gun.  WE practice USPSA under a timer.  Just before leaving we line up 12 hulls on the 26-27 yd berm and get back into both sights and careful trigger pulls with a little competition.  All three guns will shoot within an inch or so of the hulls  and pop  them UP the berm frequently standing offhand .  We spot for each other.

I guess it could be the pistol or the ammo, but I doubt it's the ammo.    Do you load other bullets like a Berry's (.356) to see if that makes a difference?

[Magsz]

No sweatskies!  I just wanted to make sure all of the pertinent info was as clear as possible.

[1SOW]

Bump to note adds to the above post.

[Riptide439]

Not familiar with the Shadow but is the barrel the same as the SP01? Could the barrel be swapped?

[Magsz]

The barrels could be swapped but due to the design im not sure if im comfortable doing that.  These barrels fit quite differently than say a Glock.

1SOW, i have not tried any .356 bullets out of either gun besides a limited amount of 147 grain BBI lead bullets.  Unfortunately, this is not an apples to apples comparison.

I am going to call CZ custom and see what they have to say and from there, potentially try some larger bullets in the shadow.

[Duckie]

Have you slugged both barrels to see if there is in fact a difference in the bore diameters? Might be worthwhile.

[Magsz]

I have not.  I dont trust myself to play with molten metal.

I think that this point, slugging the barrel is a BIT beyond me.

[painter]

You can buy slugs to check barrel size from Dardas... http://www.dardascastbullets.com/mm5/merchant.mvc?Screen=PROD&Store_Code=dardas&Product_Code=9SLUG&Category_Code=SLUGS