doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Appropriate loads for Ithaca Flues 20 bore

Do realize that when we speak of "Pressure" here we are talking "Max" chamber pressure. Push a given load to the same velocity with shells have respectively 7k & 9K psi. The 7K load will beyond all doubt have as much or more pressure out there where you hand is. The pressure curve will be different but if the same results are obtained the same work has to be done.

Light shot loads with low velocities are certainly appropriate for the Flues. As long as it has adequate wall over the chamber area don't be concerned about any pressure up to at least 9K. When we trade off to lower chamber pressure we compensate for it slightly for the rest of the barrel. Generally speaking this is not of great concern, but there is a reason that shotgun barrels are made so much "Thicker" in the chamber area.

With the advent of smokeless powders gunmakers began Beefing up the breech area of their barrels, they didn't beef up the rest of the barrel. Black powder burned slower than the early smokeless & thus had lower chamber pressure but higher barrel pressure. Believe it or not, but the gunmakers actually knew what they were doing.

I have two 20 gauge Ithaca Flues guns that I bought for parts. Both have split barrels out at the forend region. What ClapoerZapper says about the barrels being struck very thin is absolutely correct. Knowing that, I stay with low pressure loads in my two intact 20 ga. Flues guns.

That said, one buddy's younger brother used to shoot 3" magnum loads in his Dad's 20 ga. Flues without blowing up the gun. I thought that was crazy when we were in high school. But I consider him very lucky knowing what I know now.

Thanks everyone for the advice. I do know about the pressure curves for smokeless and black powders being different. I also know the relationship between chamber pressure and barrel integrity as well as payload and felt recoil. I do not see the need to hurl shot at velocities faster than 1200 FPS as they do not retain it and doing so puts undue stress on both the shooter and the gun.

That is why I am looking for proven loads from documented sources. Yes I could work up some loads that are equivalent to those in use when the gun was new but I want to preserve it as well as enjoy it, hence the low pressure and reduced payload request.

Dave

This image was posted on the PGCA site; a 20g Flues which was the sad victim of "inexpert" chamber lengthening, with a crack between the chamber and forcing cone



If the chambers are no longer 2 1/2" please have the wall thickness at the end of the (new) chamber carefully measured by someone with the interest, expertise and equipment to properly do so.

The chambers of my Flues are 2 3/4�. It also has fluid steel barrels. I�ve been told that by the serial number, the gun was made with the longer chambers. I�ve no way to verify this however. Never the less, it has been shot by the previous owner with factory RIO 2 3/4� 7/8 ounce factory loads with no ill effects as of yet. I have measured the bore diameter, thickness, chamber length and choke diameters and all appear to be within tolerances.

If the chambers were lengthened from 2 1/2� to 2 3/4� is there any benefit to shooting the shorter shell in the longer chamber?

Again, I am well aware of the potential for disaster with shooting modern �full power� loads in vintage shotguns, hence my questions. I want to develop a reduced payload, low pressure load that patterns well and will allow me enjoy shooting this little gem.

Thanks again for all of the replies and the advice.

Dave Myrick

You may have been informed incorrectly. Courtesy of David Noreen

The last Flues period catalogue (1925) states "Unless otherwise ordered Ithaca 28 Gauge and 20 Gauge guns are chambered for the standard 2 1/2 inch shell..."

Beginning with the first NID catalogue in 1926 they state -- "Unless otherwise ordered Ithaca .410 Cal. and 20 Gauge guns are chambered for the standard 2 1/2 inch shell..."

Beginning with the 1927 catalogue the sentence is changed to --"Unless otherwise ordered Ithaca .410 Cal. guns are chambered for the standard 2 1/2 inch shell, 16 Gauge for 2 9/16 inch, 20 and 12 Gauge for 2 3/4 inch and 10 Gauge for the standard 2 7/8 inch shell."

What, exactly, is the wall thickness at the end of the chambers?

Thank you for that information. I don�t have that measurement with me at the moment here at the office. I will forward it along once I get home tonight.

Assuming it is still safe to shoot, does it make a difference shooting 2 1/2� shells?

Dave Myrick

My experience was that 3/4 oz of appropriate size shot at 1100 fps will whack a South Dakota rooster out of the sky at modest distance. ymmv.

I don�t trim 2 3/4 inch hulls for my 20s do shorten 16 & 10 G hulls. It�s gun specific. 2 3/4 in a 20 with short chambers increases pressure, not a lot and within what I consider safe in my gun.

If you go short best path is a MEC 600 with the short kit. Trim or buy short hulls

Boats

As Miller pointed out, weight is an important consideration. I've weighed several Flues 20's that are a bit over 6 pounds. On the other hand, there are others that weigh in that 5 1/2# range. And as best I can recall from research a former poster here had done, the issue with those very light Flues 20's often was not with the barrel, but rather the receiver. They had a tendency to crack right where the standing breech meets the water table.

Definitely a good idea to take careful measurements of any
Flues 20 that now has 2 3/4" chambers. More critical, again, on the lighter ones--because they had thinner barrel walls to produce that light weight. And removing an extra 1/4" to lengthen the chamber could be a very big deal.

If chambers have already been lengthened to 2 3/4", then reloading those hulls to low pressure should work every bit as well as shooting 2 1/2" shells at the same pressure. The longer hull won't give you an additional pressure increase, as it will (although that increase may not be more than a few hundred psi) if fired in a 2 1/2" chamber.