I’m  working with a twelve year old CPA 38-55 Douglas 28” 16” twist, 16x Unertl. I cast the chamber and had Accurate make me a mold for a tapered breach seating 300 gr bullet. Bullet is .001” over at base band and .001” over at ogive,  alloy is 1-25 with Emmerts lube. Working with IMR 4227 and Re 7 using Fed Match primers. 4227 shows best promise right now. I don’t have enough stashed 4759 to waste on prelims. 

It’s vertical stringing a problem I’ve worked with years ago on wildcat varmint guns and hunter class BR but those were the result of hot barrels. My 38-55 sure isn’t getting hot so I need some advice on what is going on. Five shot groups start 2” low then start climbing about 2- 2.5 “ for the five shots. Some holes are touching but generally no more distance between shots than 1-1 1/2 diameters. I can see good accuracy potential but the stringing cancels that out. I’d like to think my loads are going in the right direction and the problem is my bench mechanics. I could used the collective experience and some advice.

One thing I’m not liking however is my bench set up it’s an awkward dicey looking assembly but I don’t see any easy way to benchrest a CPA with a Pope style stock and underlever and Swiss style butt plate. I made some longer threaded feet for my Hart rest to get the butt stock drop and butt plate off the deck so it’s easier to get on target. But the butt stock doesn’t play well with any of my rear bags so that needs work - longer ears. Front rest bag is a benchrest holdover that worked with flat forearmed varmint guns but I need a tighter fit for this round barrel. And of course a Swiss style butt plate is just all wrong for bench shooting though I’m sure there a quite a few of you who are forced to work with them if they shoot offhand also with one rifle.   

So what I’m suspecting is that my bench set up could probably be the source of my vertical stringing. I think the gun wants to shoot and I think I’m on the right page to dial it in but this problem has me two-blocked. I shot off the bench for lots of years and when I set up my rest and the gun it was simply a matter of lifting the bolt, reloading, sliding the rifle forward a bit and squeezing the bag a little to settle on target. Not so with this rifle it’s a wiggler and has to be convinced where to set every shot. And I haven’t found a repeatable easy way to make friends with the butt plate either. So my gut says it’s my set up and equipment and unrepeatable shooting technique.

My SWAG's would be; check your velocities and see if they are showing much variation.  Also, I found most single shot rifles to be somewhat sensitive to where you rest the barrel.  First; be consistent and second find the "dead node" location.  There was an excellent thread here a bit back on how to do that.
I did the "dead node" search on a couple of my rifles and it tempered vertical stringing for me.
Mike.

Just remembered. 

More than a few CPA Stevens rifles have been known to have very sloppy barrel shank thread to receiver fit. That can cause vertical problems.  I know of two. Re-barreled now and they shoot excellent.

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burntwater
I know what you mean about offhand butt stocks when shooting BR. My No.6 Ballard is great for OH but tricky to handle for good BR shooting.
Four things you might consider:
1. Using your current BR setup, don't use a rear bag at all. Shoulder your rifle, use your left fist under the stock perch belly. See if that helps control your vertical stringing.
2. Use a front barrel rest, one of those clamp on type works well for me. See photo below.
3. Maybe spend a little of your 4759. I have always had good luck with it in my several .38-55s over the years.
4. You are shooting a Stevens, have you made sure your butt stock is tight to the action? Stevens are a bit limp in the wrist. If it's tight, at least you'll know that's not the problem.
Good luck and please keep us posted on what works.

My early CPA 38/55 # 196 is 18 twist. It handles 300 gr bullets fine. 290 fixed or 300 breech Black & Smokless bullets I cast all it used for 20 years. 

Recently changed to 245 G store bought for high volume offhand. 245 fixed & scopes its A  1 1/2 MOA Rifle. Hand cast breech did about 1/2 MOA better. However have never campaigned the rifle in bench matches. Few bench re-entry’s before going ofhand.

Couple things . True offhand stocks don’t do well on rear bags. Best groups aways muzzle & elbow rest buttplate in My shoulder. This mirrors my Smallbore prone experience. Could shoot better 50 meter groups prone with sling than rest. Rest shooting is a different sport and takes a skill set I don’t have.  1 1/2 moa rifle is plenty good for offhand shooting. Lack of off shots make the score .

However vertical stinging is annoying and should be solved. CPA rifles are sensitive to forearm - action contact. Very good offhand shot Our club had that problem as the barrel heated up. Trimmed the forearm wood allowing a 3/5 card thickness gap cured it.

Guessing your problem is bench technique or the forearm. Also note muzzle and elbow Barrel rides the rest not the wood. Think that’s how most of the old shooters handled their guns. Take the forearm wood out of play.

John Louis on this forum has very good results with an offhand stocked CPA bench rest. Might talk on the phone with him. 

Boats

I may have overlooked this a previous post.  If so, I apologize.

A major contributor to vertical stringing is inconsistent ignition.  I've had a number of CPA rifles and I've spent time "tuning" the ignition systems on each of them.

CPA makes mainsprings with varying amounts of "stiffness" and provides an adjustment screw to add stiffness to the mainspring. CPA also makes firing pins with different physical dimensions.  Over time, I've accumulated a small supply of mainsprings and firing pins which I mix and match to achieve optimal ignition. 

You want to be sure the the firing pin has sufficient protrusion and be sure that the firing pin channel is not partially clogged with carbon fouling or brass shavings.  The mainspring should be sized and adjusted to assure that the hammer strike is neither too hard or too soft. 

The long mainspring attached at the rear of the lower tang causes a significant bending moment (torque) at the junction of the receiver and the buttstock.  Set your rifle in your rest and center the crosshairs on the target. Now cock the hammer and observe how much the crosshairs have moved.

In order to minimize vertical stringing, this bending moment has to relax exactly the same amount each time the trigger is pulled.

Accordingly, an over stressed mainspring will contribute to vertical stringing.   And, uniform relaxation of the bending moment also requires that the buttstock be a perfect fit with the receiver and that the attachment screws be snug.  A buttstock with an under or overtigtened through bolt will also contribute to vertical stringing.

I hope this helps.

JackHughs

CPA does install through bolts. Not sure it can be put into a Pope style stock.  Before I through bolted would clamp the action in a vise put a indicator on the buttstock and see if it moves when pressed. Through bolts can cure problems but not likely to improve on a properly bedded tang.

Ignition can be a problem, adjustable hammer fall facilitates switch Rimfire to CF. Has to be set so it hits hard enough not too hard. 

Boats