I’ve been doing a lot of research on shooting offhand since it’s the main limiting factor of my silhouette scores. I’m seriously considering shortening my 1874 Sharps .40-65 barrel by 4” (30” to 26”) & taking 1” off the stock to reduce the length-of-pull due to my relatively short arms. Shortening the barrel will reduce the overall weight & will move the rifle balance point closer to but still slightly forward of the forearm location where I hold it with my left hand. Since I use a scope, reducing the sight radius is not a major concern, but it will likely reduce the muzzle velocity a bit. My current BP loads result in a muzzle velocity of 1270fps. Can anyone offer an educated guess on how much the velocity will drop?

Wayne

Shiloh barrels are choked, so taking 4 inches off may affect the accuracy.
If you modify anything maybe shortening the length of pull will help, but it will also make a drastic change on your prone position.
Best bet is like Steve told you on the Shiloh forum, work on your offhand position and technique.

Well is she says so but most of mine are tighter at the muzzle than the breech... I have 8 of them...

Almost every barrel has choke to it, even when it's not designed to be choked. It simply happens since barrels are rifled from one end. That's why barrel makers mark the breech end for customers to ensure their barrels are installed correctly. Installing them backwards leads to very poor accuracy.

If you are shooting NRA rule BPCS velocity on the 200 yard chicken target is irrelevant. It’s light and any reasonable load will knock it over.

It’s sort of a not fish or fowl match. KD on Rams many worry about but until you are shooting at the highest level, winning or losing by a single target, hitting more  targets is the key. And some Rams are set so even 45/70 won’t knock down 100 % Other words working on offhand Chicken scores  is worth doing. Chicken score real separator top level vs the rest.

Stock fit is important and if too long worth the alteration. How the buttplate contacts the shoulder a key point too. BPCS rules  don’t allow much curve to the Plate. My long time BPCS rifle has as much curve as the rule allows and it helps with muzzle weight control . My # 2 rifle has a flat plate, because it switches to heavy recoil cartridges sometimes, and likes to slip if not careful . It’s best shot with a well padded vest that’s a bit sticky on the pad. Bet your 40/65 outfit is flat plate too. 

Most like a muzzle heavy rifle & all mine are, have had some too muzzle heavy and mostly added weight under the buttplate rather than reduce on the barrel end . I did have CPA re-profile a # 4 barrel to # 3 when it was just too heavy.

Far as shortening barrels, years ago Small Bore, Bolt action, silhouette shooters, all 4 critters shot offhand, believed in Short. When the rules changed favoring same gun Hunter & Silhouette rifle class majority went back to long. Overall weight rule Hunter class lower need long to get balance muzzle heavy.

Personally I think weight forward is good, both guns same overall weight don’t see any advantage short barrel vs long offhand guns. That’s opinion, not held by all.

One more. I hold my rifle thumb and forefingers front of the CPA lever, elbow on left hip. Never touch  the forearm wood. Many shooters hold front hand out on the stock elbow not supported, it’s not as steady. Close support elbow on hip awkward position until learned. After many years hip rest could not shoot well any other way. 

Boats

Although Lucinda at Shiloh assured me there was no choke in the barrel, due to Ranch's & Marlinguy's comments I just did the following.

I ran several dry & lubed real tight patch down the bore several times & no choke is evident.  So I then drove a lubed bullet about ½ way down the bore from the breech & then back out of the breech followed by driving another bullet all the way through & out the muzzle.  I could not measure a difference is either bore or groove diameter between the two bullets.  So I’m convinced my rifle does not have a choke.

Wayne

Best success would be to change the stock to a Schuetzen style.

Unfortunately the Silhouette rules state you must have the rifle's original style stock to compete in competitions.

In  Schuetzen competitions over the years I have found a heavier barrel will drop straight down over the target whereas lighter barrels start wavering in a figure eight pattern.

Best improvements for offhand practice is learning how to shoot offhand as opposed to trying to modify your firearm.

Best trick for offhand shooting is close your eyes, then open them to see where your rife is pointed.
Then move your feet to adjust your point of aim.
Most people move their position by moving their arms but this then results in muscle tension while holding the rifle that causes movement at the time of shot.
Retrain your self to hold the rifle properly so you do not incorporate muscle tension when holding the rifle.

A heavier barrel that drops straight down over the target is easier for your brain to sight with than a lighter barrel doing a figure eight dance.

Choked barrels can be shortened without affecting accuracy as long as the muzzle is properly crowned.

Ron Smith has done this for customers who use his continuously tapered barrels and it is not a problem with straight twist barrels.

However if it is a gain twist barrel the final twist may not be as tight requiring you to need to use a shorter bullet.

For Silhouette five shot strings a heavier barrel is a better choice.
However in the Schuetzen game where you have 50 shot events we do shorten the barrel due to the amount of time you have to hold the rifle.

Wayne, you’re welcome to try my Sharps. I had it cut back from 32” to 28”, but I still could not see my sights. It felt better while missing chickens. Tom